SMS - short message service

SMS is a "store and forward" system. In other words, there is a central 'post office' or service centre that receives the short message (or text message), and stores it for forwarding when the recipient mobile is in range of a signal to receive the text.  In practice this happens fairly quickly, and most users have the perception that SMS is immediate, but due to the nature it is possible to receive messages out of order.

Text messages consist of text of up to 160 characters. They are virtually universally receivable by all GSM phones (all phones released after 1998 are able to send and receive text messages).

Each text message is addressed by phone number or MSISDN, and carries the MSISDN of the sender.  Messages can be inserted from an external system directly in to the SMS centre. The SMS centres in use are from a small number of suppliers, and each supplier has their own version of the protocol for interfacing (SMPP, UCP,...).

Short codes - typically 5 digits, these shortened numbers are ideal for mass SMS input, such as TV voting or campaign responses. This type of SMS service can be arranged through a broker.