If you have the carrier information I would just send sms via email. A quick search showed the following emails by carriers:

T-Mobile phonenumber@tmomail.net 
Virgin Mobile phonenumber@vmobl.com 
Cingular phonenumber@cingularme.com 
Sprint phonenumber@messaging.sprintpcs.com 
Verizon phonenumber@vtext.com  
Nextel phonenumber@messaging.nextel.com
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I have only verified one of the addresses. It seems like it would be really easy to set this up if you can just send an email.