I recommend this from our iPhone Troubleshooting Assistant found here http://www.apple.com/support/iphone/assistant/calls/#section_2, to help troubleshoot the cellular connection. Start at step 2 and work your way down as needed. Here is the 2nd step to get you started:
Reset network settings
To reset your network settings, tap Settings > General > Reset, then scroll down and tap Reset Network Settings.
ok tried that but still the same result in the end
i think its the phone thats at fault here as i tried my simcard(giffgaff) in another phone and it works ok
phone was origanally on o2 network
i ticked the box for email notifications and ended up with hundreds of emails in my inbox
but despite changing this back i am still getting hundreds of email notifications
anyway to stop this now?
Another consideration is to verify that the phone is unlocked from the carrier.
Check out this article about unlocking the iPhone.
iPhone: About unlocking
just an update
this issue was never sorted,phone is lying doing nothing as i am using my iphone4 now with the simcard from the 5 in it and its working ok so will wait and see if its ever resolved
(using adaptor so card fits in phone)
Currently Being ModeratedJul 15, 2013 11:39 AM (in response to PC Helper)
i got the phone from friend and it was working on 02,i got giffgaff simcard as he was keeping his,now gg uses the 02 network but since i put card in it never showed a signal,so tried 02 simcard back in and it was still the same,at beginning of july i was at work and put phone on as could still browse the net and lo and behold there was full signal,so sent texts,phoned out and was working,but it went back the same way after about an hour.i dont have any cover over it,sim works in my iphone4 ok,i see many others have the same issue.