What about the regular mobile text incorporated into AIM? You can link your AIM screen name to your mobile when you are offline (away from the computer). All the messages sent to your AIM screen name goes to your phone as a text message.
http://mobile.aol.com/aolproducts/imforwarding
Only caveat is lag time variation between texts; text sometimes come in chunks as a result.
I'm sure there are other 3rd party apps that suits you better though.