prueba con esto....a mi me funcionó:
Guys.. the problem happend to me yesterday.. it happened after upgarding the iphone to 5.0.1.
The Solution is:
1- Remove the SIM card from your mobile
2- Enable the (3G & cellular Data)
3- Add the SIM card again.
4- Now .. it will working fine.
Also you can Disable the (3G & cellular Data)
I hope this fix your problem..