Short Message Service (SMS) is a communications protocol allowing the interchange of short text messages between mobile telephone devices. SMS text messaging is the most widely used data application on the planet, with 2.4 billion active users, or 74% of all mobile phone subscribers sending and receiving text messages on their phones. The SMS technology has facilitated the development and growth of text messaging. The connection between the phenomenon of text messaging and the underlying technology is so great that in parts of the world the term "SMS" is used as a synonym for a text message or the act of sending a text message, even when a different protocol is being used.

SMS as used on modern handsets was originally defined as part of the GSM series of standards in 1985 as a means of sending messages of up to 160 characters (including spaces), to and from GSM mobile handsets. Since then, support for the service has expanded to include alternative mobile standards such as ANSI CDMA networks and Digital AMPS, as well as satellite and landline networks.[citation needed] Most SMS messages are mobile-to-mobile text messages, though the standard supports other types of broadcast messaging as well.

The maximum single text message size is 160 7-bit characters even though larger content (Concatenated SMS) can be sent using 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.

The matter of addictiveness of SMS text messaging was first suggested by Nokia in its 2001 global messaging study. Ahonen in his book M-Profits in 2002 claimed that SMS was addictive and gave the reason for it to be "Reachability" ("Tavoitettavuus"). The first university study proof of the addiction was by the Catholic University of Leuven in Belgium in 2004 and a follow-up study by the Queensland University of Australia confirmed the finding and added that SMS text messaging was as addictive as cigarette smoking. Young people who suffer from SMS addiction show instances of lack of sleep (20% of youth wake up regularly to incoming SMS) and feelings of loneliness and insignificance if not receiving SMS messages. Addicted users also feel compelled to check the phone constantly to see if messages have arrived.