Steps to fixing the "Searching" for cellular service problem.
First try these basic steps:
1. Hard Reset Device
2. Reset network settings
Still not working? Heres how i just fixed one:
Remove logic board from phone. Cellular antenna is at the top left and is connect by 4 connectors. The cellular antenna grounds out on the frame of the phone which turns the entire body of the phone into an antenna. Pop the antenna off and clean all connectors and grounding points with alcohol. Reinstall and test.
Mine just had dust between the antenna and the frame of the phone.. This is likely why all of you are able to smack the phone and get service for short periods of time. The smack is closing the connection or knocking some dust off. Give it a thorough cleaning and make sure all connections go back together nice and tight and you will have a permanent fix.