So, what to do with my original iPhone when I get the new 3GS in a couple of weeks.

One thought was to put the SIM from my kid's phone in it (ATT), activate it and then somehow turn off ALL EDGE connections since he's just an add-a-line on my ATT plan and has no data access. He can use it to text, run apps and use Wifi for data, but no mobile data

possible? Is there a way to turn off all of the mobile data access?