hi i have one iphone 4 whith stranger problem , i cant make or recieve calls, the telephone works fine , internet 3g works , dont have icloud lock , dont have lock black list , dont have lock imei , but when i try to make a call , cut the call in 1 second .

another question , for try another imei is necesary change flash and cpu or can be posible change only whith a sw

iphone 4 ios 7.*.*

thank you in advance