If you want to change your iPhone's phone, and make regular calls, you now have the opportunity to do PhoneIt-IPAD. As you may recall, we wrote previously PhoneIt-IPAD when he was still under development, but now let's see what the final version has to offer.
iPhoneIslam is the developer of PhoneIt-IPAD application that turns your phone into a bar of 10 inches that can send and receive text messages and make regular calls, no problems. To use the full power of this application, you will need a 3G SIM card instead of the regular data only SIM cards you get with the iPhone, and after replacing the SIM card, you are ready for calls and send SMS messages with your iPhone. We should mention that this application requires you to have a jailbroken device IPAD, so keep that in mind.
Anyway, if you want to use your iPhone as a cell phone, only $ 20 for this app from Cydia Store and iPad jailbroken.