Get a google voice number.
Get the application.
Send text messages through data and/or wifi.
Plus you can do it all from your computer as well. 🙂
To lower the bill, I remember actually moving all of my contacts over to google voice and actually canceling my text plan last year; you can have all texts arrive in the application to either reply there or simply do it from your browser.
Saves money and allows you to send off texts a lot faster as well without having to leave the computer.
Oh and I just remembered, this would allow you to text anybody from anywhere, without needing to have a phone. And it's a free phone number to boot. For all that it offers, it can't be beat.