Apple, with AT&T, has managed to provide a very attractive unlimited data plan to use with the iPad 3G. Since the iPad 3G uses a microSIM and the iPhone uses a regular SIM, it isn’t as simple as trying to pop in the the microSIM in the iPhone SIM card tray and using the unlimited data package.
Hijinks Inc. have posted a great guide on how to get this working. You need to change the iPhone’s APN settings as well as make a sturdy adapter for the microSIM to fit in, which can then be fit into the iPhone SIM card tray. The adapter can be made out of an old credit card/plastic card etc. Also, you need to have a jailbroken iPhone since APN changer has to be installed from Cydia to change the settings. Check out our guide here to jailbreak your iPhone if you haven’t already.
The guide is pretty lengthy so head on over to the source to check it out. Or check out the video below: