I am buying a used iphone from a friend because they upgraded. I am an ATT customer. My question is this. It has some good apps and alot of music on it. If I put my simm card in it. First, will I loose the apps and music? 2nd  will it work for cell use or will I have to register it to my sim, and if so will it erase all previous apps and music? 3rd will I be able to use the itunes I have for my ipod with it, without loosing the previous apps and music, and will I be able to add music and apps without loosing what is already there?