So today I decided to take the risk and buy an iPhone4 without a contract (but locked to AT&T) and make it work with my GoPhone/Prepaid SIM card (without jail breaking).
I bought the 16gb version (599$) from the Apple store. Before doing anything with my SIM card, i simply plugged the new iPhone to my Mac, and iTunes asked for a few “I agree” clicks. Then it asked me if want to restore my old 3GS iPhone backup into my new iPhone 4. That took about 3 minutes and then the phone was up.
After that I cut my AT&T SIM card with a good pair of scissors to get the shape of the micro SIM I’ve got with the new iPhone. If you do that, you have to be carful. You might want to look at some videos on youtube before you start.
After placing my “new micro SIM” into the iPhone4 SIM slot, I waited about two seconds before getting the message I was hoping for: the iPhone activation succeeded!!
So now I could use the iPhone4 for texting and voice but no data yet. so I simply followed the same steps I wrote about a few months ago (see here) and it works! Now I have iPhone4 running with my AT&T GoPhone account, with a regular data package and without any special iPhone contract with AT&T.
I actually had to go through the process twice with another iPhone4. The first iPhone had a bad pixel so I got back to Apple and they replaced it with a new device. Then I placed my “homemade” micro SIM and the activation worked again like a charm.
**though it worked for me I can’t take any responsibility if it does not work for you :-)
UPDATE (OCT. 5th 2011): You can now get a micro sim in the ATT store instead of the regular sized card, so you dont have to cut it. They did not ask me to pay more for it. In addition, you should note that the GoPhone Unlimited plan with the unlimited data does not apply to smartphones including the iPhone (in regards to 3G Data). So you have to purchase a separate data plan (e.g. 500MB for 25$) to make the internet work for you.