Quoted:
So let me ask this questions of the iPhone experts. A very generous arfcom member gave me his old 2G iPhone to use. I mainly wanted it to run the Ballistic app and I set it up as an iTouch. It has the original SIM and I registered it on iTunes and set up an account. So it's been handy as hell just on WiFi. I use it in Airplane mode with WiFi enabled. I set up my email and figure that instead of lugging a laptop to keep up with email, I can carry the iPhone and just find a hot spot. Pandora is so good that I thinking of dumping my Sirius account. Anyway I'm unclear on just how to activate it on Tmo or another network. I assume the following:
Get a Tmo SIM
Unlock/Jailbreak iPhone
Register phone with new SIM on Tmo, configure APN?
My big question is once I Sync on iTunes with the new SIM, will I lose my apps and music downloads?
Back up your iPhone and its current settings in iTunes, insert the new SIM card and you should be able to set up a new account and restore it from the backup you just synced.
ETA: Hell, if you're just using a SIM card that's actually activated with a # from T-Mobile you can just pop it in and use it as a phone as long as it's unlocked.