[bazookaaa]

The popular (and free) thing to do is to use SMS gateways (such as sending an email to <number>@txt.att.net). See http://en.wikipedia.org/wiki/SMS_gateways

And in the future: http://searchyc.com

[unohoo]

email to sms is not pretty reliable not to mention that it imposes the requirement that you need to know the user's carrier.