Short message service

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Contents 1 History 2 Technical details 3 Premium content 4 Popularity 4.1 Europe 4.2 United States 4.3 Finland 4.4 Japan 5 Morse code 6 Spam 7 Utility 8 Text speak 9 Social impact of SMS 9.1 Academic impact 9.2 Criminal impact 9.3 Political impact 9.4 Social development 10 Vulnerabilities 11 See also 12 References 13 External links

Short Message Service (SMS) is available on most digital mobile phones and a steadily increasing range of other devices (including Pocket PC, desktop computers and some fixed phones) that permit the sending of short text messages between these devices.

The terms text messaging, text messages, more colloquially SMSes, texts, or even txts and its variants are more commonly used in North America, the UK, Spain and the Philippines, while most other countries prefer the term SMS.

Text messages are also often used to interact with automated systems, such as ordering products and services for mobile phones, or participating in contests. There are some services available on the Internet that allow users to send text messages free of direct charge to the sender, although users in other parts of the world should be aware that users of North American networks will often have to pay to receive any SMS text message.

History

As with most other services and modules of functionality of the GSM system, no individual can claim the parenthood of SMS. It might be worth while to note this, since such attempts may still be seen - also from people that never took part in the GSM work on SMS. The idea of adding text messaging to the services of mobile users was latent in many communities of mobile communication services at the beginning of the 1980s. Experts from several of those communities contributed in the discussions on which should be the GSM services. Most thought of SMS as a means to alert the individual mobile user, e.g. on incoming voice mail, whereas others had more sophisticated applications in their minds, e.g. telemetry. However, few believed that SMS would be used as a means for sending text messages from one mobile user to another.

As early as February 1985, after having already been discussed in GSM subgroup WP3, chaired by J. Audestad, SMS was considered in the main GSM group as a possible service for the new digital cellular system. In GSM document 'Services and Facilities to be provided in the GSM System' (GSM Doc 28/85 rev2, June 1985), both mobile originated and mobile terminated, including point-to-point and point-to-multipoint, short messages appear on the table of GSM teleservices.

The discussions on the GSM services were then concluded in the recommendation GSM 02.03 'TeleServices supported by a GSM PLMN'. Here a rudimentary description of the three services was given: 1) Short message Mobile Terminated / Point-to-Point, 2) Short message Mobile Originated / Point-to-Point and 3) Short message Cell Broadcast. This was handed over to a new GSM body called IDEG (the Implementation of Data and Telematic Services Experts Group), which had its kickoff in May 1987 under the chairmanship of Friedhelm Hillebrand. The technical standard known today was largely created by IDEG (later WP4) as the two recommendations GSM 03.40 (the two point-to-point services merged together) and GSM 03.41 (cell broadcast).

The first commercial SMS message was sent over the Vodafone GSM network in the United Kingdom on 3 December 1992, from Neil Papworth of Sema Group (using a personal computer) to Richard Jarvis of Vodafone (using an Orbitel 901 handset). The text of the message was "Merry Christmas". The first SMS typed on a GSM phone is claimed to have been sent by Riku Pihkonen, an engineer student at Nokia, in 1993.

Initial growth was slow, with customers in 1995 sending on average only 0.4 messages per GSM customer per month. [1] One factor in the slow takeup of SMS was that operators were slow to set up charging systems, especially for prepaid subscribers, and eliminate billing fraud which was possible by changing SMSC settings on individual handsets to use the SMSCs of other operators. Over time, this issue was eliminated by switch-billing instead of billing at the SMSC and by new features within SMSCs to allow blocking of foreign mobile users sending messages through it. An example of a company that innovate in this subject is OsinetS.A.. By the end of 2000, the average number of messages per user reached 35.

It is also alleged that the fact that roaming customers, in the early days, rarely received bills for their SMSs after holidays abroad had a boost on text messaging as an alternative to voice calls.

SMS was originally designed as part of GSM, but is now available on a wide range of networks, including 3G networks. However, not all text messaging systems use SMS, and some notable alternate implementations of the concept include J-Phone's SkyMail and NTT Docomo's Short Mail, both in Japan. E-mail messaging from phones, as popularized by NTT Docomo's i-mode and the RIM BlackBerry, also typically use standard mail protocols such as SMTP over TCP/IP.

Technical details

The Short Message Service - Point to Point (SMS-PP) is defined in GSM recommendation 03.40. GSM 03.41 defines the Short Message Service - Cell Broadcast (SMS-CB) which allows messages (advertising, public information, etc.) to be broadcast to all mobile users in a specified geographical area.

Messages are sent to a Short Message Service Centre (SMSC) which provides a store-and-forward mechanism. It attempts to send messages to their recipients. If a recipient is not reachable, the SMSC queues the message for later retry. Some SMSCs also provide a "forward and forget" option where transmission is tried only once. Both Mobile Terminated (MT), for messages sent to a mobile handset, and Mobile Originating (MO), for those that are sent from the mobile handset, operations are supported. Message delivery is best effort, so there are no guarantees that a message will actually be delivered to its recipient and delay or complete loss of a message is not uncommon, particularly when sending between networks. Users may choose to request delivery reports, which can provide positive confirmation that the message has reached the intended recipient, but notifications for failed deliveries are unreliable at best.

Transmission of the short messages between SMSC and phone can be done through different protocols such as SS7 within the standard GSM MAP framework or TCP/IP within the same standard. Messages are sent with the additional MAP operation forward_short_message, whose payload length is limited by the constraints of the signalling protocol to precisely 140 bytes (140 bytes = 140 * 8 bits = 1120 bits). In practice, this translates to either 160 7-bit characters, 140 8-bit characters, or 70 16-bit characters. Characters in languages such as Arabic, Chinese, Korean, Japanese or Slavic languages (e.g. Russian) must be encoded using the 16-bit UCS-2 character encoding (see Unicode). Routing data and other metadata is additional to the payload size.

Larger content (known as long SMS or concatenated SMS) can be sent segmented over multiple messages, in which case each message will start with a user data header (UDH) containing segmentation information. Since UDH is inside the payload, the number of characters per segment is lower: 153 for 7-bit encoding, 134 for 8-bit encoding and 67 for 16-bit encoding. The receiving phone is then responsible for reassembling the message and presenting it to the user as one long message. While the standard theoretically permits up to 255 segments, 6 to 8 segment messages are the practical maximum, and long messages are billed as equivalent to multiple SMS messages.

Short messages can also be used to send binary content such as ringtones or logos, as well as OTA programming or configuration data. Such uses are a vendor-specific extension of the GSM specification and there are multiple competing standards, although Nokia's Smart Messaging is by far the most common.

The SMS specification has defined a way for an external Terminal Equipment, such as a PC or Pocket PC, to control the SMS functions of a mobile phone. The connection between the Terminal Equipment and the mobile phone can be realized with a serial cable, a Bluetooth link, an infrared link, etc. The interface protocol is based on AT commands. Common AT commands include AT+CMGS (send message), AT+CMSS (send message from storage), AT+CMGL (list messages) and AT+CMGR (read message).

Some service providers offer the ability to send messages to land line telephones regardless of their capability of receiving text messages by automatically phoning the recipient and reading the message aloud using a speech synthesizer along with the number of the sender.

Today, SMS is also used for machine to machine communication. For instance, there is an LED display machine controlled by SMS, and some vehicle tracking companies like ESITrack use SMS for their data transport or telemetry needs. SMS usage for these purposes are slowly being superseded by GPRS services due to their lower overall costs.

Premium content

SMS is widely used for delivering digital content such as news alerts, financial information, logos and ringtones. Such messages are also known as premium-rated short messages (PSMS). The subscribers are charged extra for receiving this premium content, and the amount is typically divided between the mobile network operator and the value added service provider (VASP) either through revenue share or a fixed transport fee.

Premium short messages are increasingly being used for "real-world" services. For example, some vending machines now allow payment by sending a premium-rated short message, so that the cost of the item bought is added to the user's phone bill or subtracted from the user's prepaid credits. Recently, premium messaging companies have come under fire from consumer groups due to a large number of consumers racking up huge phone bills. Some mobile networks, now require users to call their provider to enable premium messages from reaching their handset.

A new type of 'free premium' or 'hybrid premium' content has emerged with the launch of text-service websites. These sites allow registered users to receive free text messages when items they are interested go on sale, or when new items are introduced.

Popularity

Short message services are developing very rapidly throughout the world. In 2000, just 17 billion SMS messages were sent; in 2001, the number was up to 250 billion, and 500 billion SMS messages in 2004. At an average cost of USD 0.10 per message, this generates revenues in excess of $50 billion for mobile telephone operators and represents close to 100 text messages for every person in the world.

SMS is particularly popular in Europe, Asia (excluding Japan; see below), Australia and New Zealand. Popularity has grown to a sufficient extent that the term texting (used as a verb meaning the act of mobile phone users sending short messages back and forth) has entered the common lexicon. In China, SMS is very popular, and has brought service providers significant profit (18 billion short messages were sent in 2001 [2]). It is a very influential and powerful tool in the Philippines, where the average user sends 10-12 text messages a day. The Philippines alone sends on the average 400 million text messages a day, more than the annual average SMS volume of countries in Europe, and even China. SMS is hugely popular in India, where youngsters often exchange lots of text messages, and companies provide alerts, infotainment, news, cricket scores update, railway/airline booking, mobile billing, and banking services on SMS. In India, metropolitan media outlets often take real-time polls and audience opinion through SMS, via reserved 4-digit numbers that redirect the information to the respective aforementioned outlets based on designated prefix codes.

Short messages are particularly popular amongst young urbanites. In many markets, the service is comparatively cheap. For example, in Australia a message typically costs between AUD 0.20 and AUD 0.25 to send (some pre-paid services charge AUD 0.01 between their own phones), compared with a voice call, which costs somewhere between AUD 0.40 and AUD 2.00 per minute (commonly charged in half-minute blocks). Despite the low cost to the consumer, the service is enormously profitable to the service providers. At a typical length of only 190 bytes (incl. protocol overhead), more than 350 of these messages per minute can be transmitted at the same data rate as a usual voice call (9 kbit/s).

Text messaging has become so popular that advertising agencies and advertisers are now jumping into the text message business. Services that provide bulk text message sending are also becoming a popular way for clubs, associations, and advertisers to quickly reach a group of opt-in subscribers. This advertising has proven to be extremely effective, but some insiders worry that advertisers may abuse the power of mobile marketing and it will someday be considered spam.

Europe

Europe follows next behind Asia in terms of the popularity of the use of SMS. In 2003, an average of 16 billion messages were sent each month. Users in Spain sent a little more than fifty messages per month on average in 2003. In Italy, Germany and the United Kingdom the figure was around 35–40 SMS messages per month. In each of these countries the cost of sending an SMS message varies from as little as £0.03–£0.18 depending on the payment plan. Curiously France has not taken to SMS in the same way, sending just under 20 messages on average per user per month. France has the same GSM technology as other European countries so the uptake is not hampered by technical restrictions.

In Ireland, a total of 1.5 billion messages are sent every quarter, on average 114 messages per person per month. [3]

The Eurovision Song Contest organized the first pan-European SMS-voting in 2002, as a part of the voting system (there was also a voting over traditional phone lines). In 2005, the Eurovision Song Contest organized the biggest televoting ever (with SMS and phone voting).

United States

In the United States, however, the appeal of SMS is more limited. Although an SMS message usually costs only US$0.15 (many providers also offer monthly text messaging plans), only 13 messages were sent by the average user per month in 2003. In the US, SMS is often charged both at the sender and at the destination, but it cannot be rejected or dismissed, as opposed to the phone calls. The reasons for this are varied—many users have unlimited "mobile-to-mobile" minutes, high monthly minute allotments, or unlimited service. Moreover, push to talk services offer the instant connectivity of SMS and are typically unlimited. Furthermore, the integration between competing providers and technologies necessary for cross-network text messaging has only been available recently. Some providers originally charged extra to enable use of text, further reducing its usefulness and appeal. The relative popularity of e-mail-based devices such as the BlackBerry in North America may be a response to the weakness of text messaging there, but these further weaken the appeal of texting among the users most likely to use it. However the recent addition of Cingular-powered SMS voting on the television program American Idol has introduced many Americans to SMS, and usage is on the rise.^{[citation needed]}In the third quarter last year (2006), more than 10 billion text messages crossed Cingular's network, up almost 15 percent from the preceding quarter.

Finland

In addition to SMS voting, a different phenomenon has risen in more mobile-phone-saturated countries. In Finland some TV channels began "SMS chat", which involved sending short messages to a phone number, and the messages would be shown on TV a while later. Chats are always moderated, which prevents sending harmful material to the channel. The craze soon became popular and evolved into games, first slow-paced quiz and strategy games. After a while, faster paced games were designed for television and SMS control. Games tend to involve registering one's nickname, and after that sending short messages for controlling a character on screen. Messages usually cost 0.05 to 0.86 Euro apiece, and games can require the player to send dozens of messages. In December 2003, a Finnish TV-channel, MTV3, put a Santa character on air reading aloud messages sent in by viewers. More recent late-night attractions on the same channel include "Beach Volley", in which the bikini-clad female hostess blocks balls "shot" by short message. On March 12 2004, the first entirely "interactive" TV-channel "VIISI" began operation in Finland. That did not last long though, as SBS Finland Oy took over the channel and turned it into a music channel named "The Voice" in November 2004.

In 2006, the Prime Minister of Finland, Matti Vanhanen, made front page news when he allegedly broke up with his girlfriend with a text message.

In 2007, the first text message only book, which is about a business executive who travels throughout Europe and India, was published by a Finnish author.

Japan

Japan was among the first countries to widely adopt short messages, with pioneering non-GSM services including J-Phone's SkyMail and NTT Docomo's Short Mail. However, short messaging has been largely rendered obsolete by the prevalence of mobile Internet e-mail, which can be sent to and received from any e-mail address, mobile or otherwise. That said, while usually presented to the user simply as a uniform "mail" service (and most users are unaware of the distinction), the operators may still internally transmit the content as short messages, especially if the destination is on the same network.

Morse code

A few widely publicised speed contests have been held between expert Morse code operators and expert SMS users (see references). Several mobile phones have Morse code ring tones and alert messages. For example, many Nokia mobile phones have an option to beep "S M S" in Morse code when it receives a short message. Some of these phones could also play the Nokia slogan "Connecting people" in morse code as a message tone. There are third-party applications available for some mobile phones that allow Morse input for short messages (see references).

Spam

In 2002, an increasing trend towards spamming mobile phone users through SMS prompted cellular service carriers to take steps against the practice, before it became a widespread problem. No major spamming incidents involving SMS had been reported as of March 2007, but the existence of mobile-phone spam has been noted by industry watchdogs, including Consumer Reports magazine and the Utility Consumers' Action Network (UCAN). In 2005, UCAN brought a case against Sprint for spamming its customers and charging $0.10 per text message [4]. The case was settled in 2006 with Sprint agreeing not to send customers Sprint advertisements via SMS[5].

SMS expert LogicaCMG reported a new type of SMS-malice at the end of 2006, noting the first instances of SMiShing (a cousin to email phishing scams). In SMiShing, users receive SMS messages posing to be from a company, enticing users to phone premium rate numbers, or reply with personal information.

Utility

SMS has also given people instant access to a wealth of information. Services like 82ASK and Any Question Answered in the UK have used the SMS model to enable rapid response to mobile consumers' questions, using on-call teams of experts and researchers.

Text speak

See main article: SMS language.

The small phone keypad caused a number of adaptations of spelling, as in the phrase "txt msg", or use of CamelCase, such as in "ThisIsVeryCool". To avoid the even more limited message lengths allowed when using Cyrillic or Greek letters, speakers of languages written in those alphabets often use the Latin alphabet for their own language.

Historically, this language developed out of shorthand used in Bulletin Board Systems and later in internet chatrooms, where users would abbreviate some words to allow a response to be typed more quickly. However, this became much more pronounced in SMS, where mobile phone users don't generally have access to a QWERTY keyboard as computer users did, more effort is required to type each character, and there is a limit on the number of characters that may be sent.

In Mandarin Chinese, numbers that sound similar to words are used in place of those words. For example, the numbers 520 in Chinese ("wu er ling") sound like the words for "I love you" ("wo ai ni"). The sequence 748 ("qi si ba") sounds like the curse for "drop dead".

Predictive text software that attempts to guess words (AOL/Tegic's T9 as well as iTAP) or letters (Eatoni's LetterWise) reduces the labour of time-consuming input. This makes abbreviations not only less necessary, but slower to type than regular words which are in the software's dictionary. However it does make the messages longer, often requiring the text message to be sent in multiple parts and therefore costing more to send.

Website portals such as transl8it have supported a community of users to help standardize this text speak by allowing users to submit translations, staking claim with their user handle, or to submit top messages and guess the lingo phrases. The international popularity of this portal resulted in late 2005 the publishing of the transl8it! dxNRE & glosRE (dictionary & glossary) as the worlds first, and most complete, SMS and text lingo book.

Social impact of SMS

SMS has caused subtle but interesting changes in society and language since it became popular. News-worthy events include (in chronological order):

Academic impact

• In December 2002, a cheating scheme was uncovered during final-exam week at the University of Maryland, College Park. A dozen students were caught cheating on an accounting exam through the use of text messages on their mobile phones.
• In December 2002, Hitotsubashi University in Japan failed 26 students for receiving e-mailed exam answers on their mobile phones.
• Using text language is becoming an increasing practice in classes and exams.[6]

Criminal impact

• In October 2001, a Filipino immigrant living in Belgium was arrested by police after a friend sent him a joke short message pretending to be Osama bin Laden. The message read "I was wondering if I can stay with you for a couple of days. Everybody's so angry with me. I really need a friend. Yours truly, Osama bin Laden." [7].
• In June 2003, a British company developed a program called Fortress SMS for Symbian phones which used 128 bit Rijndael encryption to protect SMS messages.[8].
• In January 2004, cult member Sara Svensson confessed to having murdered the wife of pastor Helge Fossmo and having shot his lover's husband Daniel Linde in Knutby, Sweden. She said that she had acted on anonymous text messages that the pastor had forwarded to her. [9]
• In June 2004, a British punk rock fan was questioned by police regarding a text message sent to a wrong number containing lyrics from "Tommy Gun" by The Clash: "How about this for Tommy Gun? OK - so let's agree about the price and make it one jet airliner for 10 prisoners." [10].
• In July 2004, the police in Tilburg, the Netherlands, started an experiment in which people could register for a short message service. The police would send a message to ask citizens to be vigilant when a burglar was on the loose or a child was missing in their neighbourhood. Several thieves have been caught and children found using the "SMS Alerts". The service has been expanding rapidly to other cities.
• On August 14, 2005, there was a hoax involved in the Helios Airways Flight 522 plane crash. News media widely reported that shortly before the crash a passenger sent a short message indicating that the pilot had become blue in the face, or roughly translated as "The pilot is dead. Farewell, my cousin, here we're frozen." Police later arrested Nektarios-Sotirios Voutas, a 32 year-old private employee from Thessaloniki who admitted that he had made up the story and given several interviews in order to get attention.
• In December 2005, ChinaTechNews.com reported that China's Beijing police detained nine suspects who were members of an illegal wireless short message-sending organization called "Xiao Hai". Local media reported that the suspects included a person surnamed Zou who had been involved in organizing homosexual prostitution, and Wang Wenbin who police say is guilty of bank fraud.[11].
• In February 2005, an Australian company by the name of theSMSzone.com launched a controversial SMS spoofing service allowing messages to be masked, anonymous, and thus totally unidentifiable. This facilitates spam, mobile fraud and defamation, among other things.
• In December 2005 in Australia, text messaging was cited for helping to incite the 2005 Cronulla riots. The SMS messages assisted in mobilising about 5,000 white Australians to engage in violence against those of Middle Eastern origin. In response, some Australians have called for the use of text messaging (or any other electronic means) to incite a riot to be treated as an aggravating circumstance and thus punished more harshly than other forms of incitement.

Political impact

• In January 2001, Joseph Estrada was forced to resign from the post of president of the Philippines. The popular campaign against him was widely reported to have been co-ordinated with SMS chain letters.
• In the wake of the 2004 Madrid train bombings, SMS was used to garner support for large protest rallies.
• During the 2004 US Democratic and Republican National Conventions, protestors used an SMS based organizing tool called TXTmob.
• During the 2004 Philippine presidential elections, short message was a popular form of electoral campaigning for and against candidates such as incumbent president Gloria Macapagal-Arroyo and main contender Fernando Poe, Jr.
• In March of 2005, SMS was one of the communications forms used to garner support for the Lebanese political rallies.
• French national police spokesman, Patrick Hamon, was quoted in the Wall Street Journal as saying that during the 2005 civil unrest in Franceyouths in individual neighborhoods were communicating by cellphone text messages, online blogs, and/or email — arranging meetings and warning each other about police operations.
• The Islamic Republic of Iran disabled their nationwide SMS network during the 2005 Iranian Presidential elections in which Mahmoud Ahmadinejad was elected President. Some Western commentators have suggested that this was orchestrated to help get Ahmadinejad elected and to quell political uprising.
• Political organisations such as Cymru X, the Plaid Cymru youth wing, and the Young Scots for Independence, the youth wing of the Scottish National Party, have used a "text referendum" to gain public support and raise the profile of their respective causes. The YSI are currently running text referenda on Scottish independence, nuclear weapons, and a St Andrew's Day public holiday.
• In 2006, the Scottish Socialist Party initiated a campaign for people to text the First minister Jack McConnell to demonstrate their support for free school meals.
• SMS messages were used by Chinese nationalists to rapidly spread word of the time and location of demonstrations during the 2005 anti-Japanese demonstrations. At the time, it was one of the few electronic media in China that was not subject to direct government monitoring.

Social development

• In July 2001, Malaysia's government decreed that an Islamic traditional divorce (which consists of saying "I divorce you" three times in succession) was not valid if sent by short message.
• In 2003, a Malaysian court ruled that, under Sharia law, a man may divorce his wife via text messaging as long as the message was clear and unequivocal. [12]
• In 2003, 2500 employees of the British Amulet Group were fired via a text message to their mobile phone.[13] A similar, widely reported incident occurred in Cardiff, Wales in July 2006.[14][15]
• In August 2005, an SMS chat sculpture was installed at the annual diploma exhibition of Dresden's University of Art HfBK. The artist Matthias Haase explores today's means of social interaction. Visitors may participate in the art work by sending a text message to the sculpture, which projects the message onto a screen [16].
• During Hurricane Katrina in August 2005, many residents were unable to make contact with relatives/friends using traditional landline phones. Via SMS they could communicate with each other when the network worked.^{[citation needed]}
• In November 2006, New Zealand Qualifications Authority approved the move that allowed students of secondary schools to use mobile phone text in the end of the year exam papers. [17]

• In November 2006, Britney Spears reportedly used text messaging to tell her husband Kevin Federline that she is filing for a divorce, however the official divorce filing only occurred the day after the text message was sent. The story was reported by various news media outlets. [18]
• Guinness Book of World records has a world record for text message, currently held by Ang Chuang Yang of Singapore

• Ms. Ang keyed in the official text messaging sentence, as established by Guinness (“The razor-toothed piranhas of the genera Serrasalmus and Pygocentrus are the most ferocious freshwater fish in the world. In reality they seldom attack a human.”), in 41.52 seconds.

Vulnerabilities

• In October 2005, researchers from Pennsylvania State University published an analysis of vulnerabilities in SMS-capable cellular networks.

See also

• 3rd Generation Partnership Project (3GPP)
• Common Short Code
• BlackBerry
• Enhanced Messaging Service (EMS)
• GoText (SMS messaging application)
• Luscious SMS (SMS messaging application for Mac OS X)
• Instant message
• Multimedia Messaging Service (MMS) (a newer standard)
• Mobile Marketing
• Shorthand
• Short Message Service Center (SMSC)
• Short Message Peer-to-Peer (SMPP)
• SMS/800 (Service Management System Toll Free Database)
• SMS gateways (sending SMSes to or from devices other than cellphones)
• Speedwords
• Reverse SMS billing
• Gps2sms (sending SMSes containing GPS coordinates)
• Mobile development
• WAP

References

• Je ne texte rien, The Economist, July 10, 2004 (page 65 UK edition)
• Nokia files patent for Morse Code-generating cellphone, March 12, 2005, Engadget.
• A race to the wire as old hand at Morse code beats txt msgrs, April 16, 2005, The Times Online.
• Nokia app lets you key SMSes in Morse Code, June 1, 2005 Boing Boing.
• Back to the Future - Morse Code and Cellular Phones, June 28, 2005 O'Reilly Network.
• 2500 People Fired by Text Message, May 30, 2003, The Inquirer

External links

• 3GPP - The organization that maintains the SMS specification.
• SMS Forum - The organization that maintains the SMPP protocol.
• SMS, the strange duckling of GSM (PDF format)
• ISO Standards (In Zip file format)
• Information on Text Messaging SMS Services and how they work