SMS stands for Short Message Service , and SMS messages are indeed short: each message cannot be longer that 160 alphanumeric characters (i.e., numbers, letters, and punctuation).
SMS was originally developed as a technology to transfer text messages to wireless pagers, but has gradually evolved into something much more versatile. Many wireless pagers with SMS functionality allow users to compose and send messages back and forth from the same device, thereby can be used to chat with short text messages.
Currently, there are many devices that can send and receive
SMS messages: cellular phones, pagers, text paging devices, and even PDAs.
SMS messages can also be transmitted across the Internet. For instance,
ICQ allows you to send SMS messages to wireless devices and some wireless
devices allow you to send SMS messages to an Internet e-mail address.