Need Help Switching iPhone Sim to Pre-Paid Phone

[maddan]

Is it possible to take the SIM Card out of the iPhone, and put it into a pre-paid phone? When I called AT&T, they said I could, but that I needed the IMEI. What's it for? And whose IMEI do I need? The pre-paid phone's or the iPhone's?
Thanks in advance!

 

[Karel Roos]

Theres an easier way to make your iphone into a pre paid phone. I turned my iphone 2g into a go phone, and all i had to do was to use the program redsn0w. You can also use redsn0w to jailbreak your iphone, but if you dont want to do that just deselect it when it asks you if you want to.

hope this helps