best bet is to go with a voip provider (one example may be...

best bet is to go with a voip provider (one example may be mynetfone), where you are able to sms through their web interface. Not to mention that voip for phone calls is extremely cost effective as well. That said, if you only wanted their sms capability, you don't need to worry about voip. The most basic level of service from them would cost you around $5 a month, plus sms's.