List of SMS Email Extensions

Verizon Wireless
The email extension for Verizon Wireless users is '@vtext.com'---add this extension after the full cell-phone number. When you send a text message to a Verizon customer you have a 160-character limit per text---any email you send longer than that will separate into two or more messages.
AT&T Wireless
You can reach an AT&T Wireless cell-phone account holder by emailing the phone number followed by 'txt.att.net.' Like Verizon, AT&T also has a 160 character limit on each text message. Keep in mind that AT&T Wireless now includes former customers from Alltel and Cingular.
Sprint
Sprint, which merged with Nextel in 2005, has two different extensions for subscribers. Before you attempt to send your message, find out if the person you want to text is a former Nextel customer first. Use '@messaging.sprintpcs.com' to send a text message via email to a Sprint user and '@messaging.nextel.com' if it's a former Nextel customer. In either case, the message size limit is 500 characters for Sprint (and Nextel) users.
T-Mobile
T-Mobile, another popular mobile service, also allows you to send short messages via email. If you need to send your text message via T-Mobile, type '@tmomail.net' after the full cell-phone number. T-Mobile permits 160 characters per text.