John’s iPhone works fine on the T-mobile EDGE network. Just use these settings:

Settings -> General -> Network -> EDGE

APN: internet2.voicestream.com
username: blank
password:  blank

The only issue we had with this was after we had put a Dutch (Vodafone) sim card in the iPhone and then put back the T-mobile sim card, the EDGE settings went back to the original cingular settings. So, we had to manually change them back.