Iphone 4 keeps saying No Service?

I sent my brothers iphone that had a damaged screen(but the mobile network was working completely fine) so I went to a phone repair shop to fix the screen and they fixed the screen, but there was no network connection atall it keeps saying "No Service"? What is going on? Did the shop accidently mess the phone up?

No service is an extremely common iPhone fault, which is usually user-caused.
However, if it was working when you handed it in for repair, then the shop has caused the fault by damaging the aerial in some way.