Short Messaging Service, otherwise known as text messaging, mobile messaging, or alphanumeric paging is a digital cellular network feature. It lets you send short text and numeric messages to and from digital cell phones, cell phones and e-mail addresses, as well as cell phones and public SMS messaging gateways on the Internet.

SMS is convenient and cost effective for a number of reasons. When you compare it with the cost of airtime for voice calls or wireless web access, SMS is a real bargain. Messages can be received while making voice calls, and there are no busy signals to contend with. Plus, if you should you find yourself in a situation where talking on a cell phone is inappropriate, SMS is silent and discreet. Messages generated by SMS are immediately delivered directly to your phone. There is no need to call an access number, as is the case with voice-mail. Also, most carriers offer SMS alerts (information packets, such as stock quotes, sports scores, and news) that can be delivered to your phone at regularly scheduled intervals.

Currently, there are approximately 30 billion SMS messages sent globally each month, with the majority of that traffic occurring in Western Europe and Asia. In North America most major cellular providers offer either one-way or two-way SMS to their subscribers. With one-way service, you can receive messages; while with two-way service, you can both receive and send messages.

The Short Message Service (SMS), as defined within the GSM digital mobile phone standard has several unique features:

    *      A single short message can be up to 160 characters of text in length. Those 160 characters can comprise of words or numbers or an alphanumeric combination. Non-text based short messages (for example, in binary format) are also supported. These are used for ringtones and logos services for instance.
    *      The Short Message Service is a store and forward service, in other words, short messages are not sent directly from sender to recipient, but always via an SMS Center instead. Each mobile telephone network that supports SMS has one or more messaging centers to handle and manage the short messages.
    *      The Short Message Service features confirmation of message delivery. This means that unlike paging, users do not simply send a short message and trust and hope that it gets delivered. Instead the sender of the short message can receive a return message back notifying them whether the short message has been delivered or not.
    *      Short messages can be sent and received simultaneously with GSM voice, Data and Fax calls. This is possible because whereas voice, Data and Fax calls take over a dedicated radio channel for the duration of the call, short messages travel over and above the radio channel using the signaling path. As such, users of SMS rarely if ever get a busy or engaged signal as they can do during peak network usage times.
    *      Ways of sending multiple short messages are available. SMS concatenation (stringing several short messages together) and SMS compression (getting more than 160 characters of information within a single short message) have been defined and incorporated in the GSM SMS standards.

I also love to reply my friends, I have more than 30 sms at a time in my mobile, Daily i reeive more than 30 sms, i spend large money to send sms to friends, I want this service should be free.

cal its more expensive to talk to them so just sms them its a few pennys cheaper