Hi, I just had the same problem with my iphone 4. Basicly, i had bought a phone on the craiglist. the seller was lited to me "New iphone in box" he said.
After that. i had used an found the signal of wifi is good, signal of phone was alway searched, low & off. i could not made the called, even could not received the call. and the phone was over heat!. some time, it was die by it self! And finally it could be not working with iTune!!!... i was called him, and all you know?.. He was never picked up the phone!
The lesson i was learned 400 of dollars even!.
after that, i had given to iPhone repair shop. was paid 50, & 70, & 100, for jailbroken and unlocked: for it time the phone's justed worked half of a day, full day, and some day was max.
Well well, I was so tire i am. Yesterday i was started to studied and i have to fixing by myself!!!. I am going to diagnosting and trouble shooting. i will let you know what i get. i just worry from where may i buy the parts as mother...et. Please do give me some place they have good parts for iphone 4 32gb and may i update to 46gb?. Thanks for have been reading and help> see you next post. Loc tran 052812