SMS Messaging Networks
Whenever you send a text message from your mobile phone it goes
through a network provided by your cellular network of choice.
Virtually all of the major wireless networks in North America
have some sort of message center, which routes text messages to
make sure they make it from sender to receiver.
SMS messages are by definition very short (under 160
characters), meaning that they use up very little bandwidth when
compared with regular voice calls.
The SMS text
messaging format was originally designed for use with GSM
(Global System for Mobile) networks, but has since been extended
to more advanced wireless technologies, including high-speed 3G
networks.