I arrived in India with my european phone number and all it says was “no service” and “restricted network”. I went nuts because i tried resetting, restarting, pulling up simcard and reinserting but nothing worked. Then bingo! it worked easy and realized that iphone has issue with switching from airplane mode. huh!
Here is what you have to do to fix this issue:
1. Disable 3g
2. Switch the airplane mode to OFF and then back ON.
Your phone should get picking up the signal, if you are roaming or whatever. Good luck!