AT&T customers reportedly don't have to worry about their gophone SIM cards or their non-iphone plan SIM cards not working. What's the deal? The latest software version 2.0.
In the good old days AT&T users were required to use the iPhone sim that came in the box and activate their accounts via iTunes also agreeing to a 2 year contract on data prices while they were at it. Many users chose to dig a little deeper and decided to jailbreak their 1st gen phones and then play around a bit with unlocking and activation in order to use their iPhones at cheaper carrier prices.
With firmware version 2.0 switching between ANY AT&T SIM card is easy. On the 3g iPhone you just pop it in and it works. The 1st generation iPhone is a bit more tedious, but no a big deal. It requires you to connect to iTunes to be activated, but unlike the past it will activate.
Furthermore it is reported that the 3g iPhone works just fine with a gophone sim at the cheap rate of $20/mo
Edit: Contrary to the results discovered by phonenews some of our members say this doesn't work with first generation phones even after the 2.0 upgrade. It seems to work on the 3g phone just fine. Beware.