network stay on searching and warm my phone

Hi to all this has been more than 4 months now not having any network signal! just displaying searching and keep warming my phone. i changed the antenna, tried different type of sim card, but still the same thing no network i tried to change the ios to 7 and now 8, still the same but the funny thing is when i had to activate the phone thru iTunes it has recognized that there is a sim card and unlocked my phone. Any help please? thank in advance.