Testing SMS code without access to a texting plan

Google now has the answer for which I seek. With the roll-out of their new Google Voice (previously GrandCentral) they added the ability to received text messages to the phone number (which currently is free). While technically somewhat of a text plan, one could theoretically sign up for a few accounts and be able to test multiple phone numbers.

http://www.google.com/voice/

Update (Nov 2010): Perhaps an even better way to do this now is to use either Tropo (tropo.com) or Twilio (twilio.com). Both of them offer low cost SMS messaging and Tropo is free for development. I've been using Tropo and it's very quick and easy to setup and write and code for.