Short messaging service (SMS) is the technical name for a variety of common cellphone functions, most notably text-messaging. SMS short code is a special type of SMS message that typically tells a remote system to perform a certain action. These codes are often used as part of a voting, subscription or other automated service and basically involve any circumstance when a person needs to activate a non-human system. An SMS short code is not always covered by the same plan as standard text messaging and may require additional fees per use.
SMS short code was originally developed as a way to transfer premium content to individuals without having to set up external subscription plans. Using the short codes implied an agreement between the user, his phone service and a third-party service. The short code would cost additional money to use, and that amount would be added directly to the user’s phone bill. The additional cost would be split between the phone carrier and the third party.
The initial use of SMS short code was downloading ringtones. It didn’t take long for additional uses to pop up, some of the first being other cellphone-related services like games and background wallpaper. Later, voting systems for television shows and sweepstakes entries also became common. Full-on subscription services have also become commonplace. A user will send out an SMS short code, and then they will receive periodic messages or downloads from a company for a reoccurring monthly fee.
Short codes work due to an oddity in the phone system. A phone number may be nearly any amount of numbers. The standard American phone number consists of 11 numbers; other countries may have more or less. When a phone is dialed from a land line, the entire number must be dialed. Cell phone systems do not require this, because numbers are considered "finished" when the caller hits the "send" button.
The format for short codes varies by location. Nearly every country that has a short code format requires that the code be longer than three digits. Shorter codes are often part of the internal systems for the cellphone carrier involved with calling a voicemail system or checking account balances.
Most countries have a central database that issues short codes. This is done to prevent overlap and to allow different countries to keep recognizable formats. To maintain formatting, many areas have restrictions on what number the short code may start with and how many digits it must have. When combined with standard international phone protocol, it is possible to use SMS short code in a standard long distance format.