The Full form of SMS is Short Message Service. SMS is an acronym for Short Message Service. It is a form of text-messaging communication based on phones and mobile phones. It is a communication protocol that allows exchanging text messages between mobile devices. You can send SMS by mobile phones, smartphones, computer systems with the web, handheld devices etc. All telecommunication companies like Vodafone, Airtel, Idea, Aircel, Reliance, BSNL etc. provide the facility of sending SMS. With an estimated 3.5 billion active users, SMS is the most widely used data application. It was originally designed as a part of GSM, but is now available on the CDMA phones also. The maximum length of an individual message goes up to 160 alpha-numeric 7 bits characters. (In the case of 5-bit mode, it supports 224 characters). An SMS message is stored temporarily in the SMS centre if the recipient mobile phone is unavailable. It is possible on most mobile handset to specify an expiry period after which the SMS message will be deleted from the SMS centre. Once deleted, the SMS message will no longer be available for dispatch to the recipient mobile phone (even if it becomes online).