Here are some Major Phone Carrier Company examples of how to format an email to go to someones phone as a SMS Text Message.
Alltel
[10-digit phone number]@message.alltel.com
AT&T (formerly Cingular)
[10-digit phone number]@txt.att.net
Boost Mobile
[10-digit phone number]@myboostmobile.com
Nextel (now part of Sprint Nextel)
[10-digit telephone number]@messaging.nextel.com
Sprint PCS (now Sprint Nextel)
[10-digit phone number]@messaging.sprintpcs.com
T-Mobile
[10-digit phone number]@tmomail.net
Verizon
[10-digit phone number]@vtext.com
Virgin Mobile USA
[10-digit phone number]@vmobl.com