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