Settings > General > Reset > Reset Network Settings.
Basic troubleshooting from the User's Guide is reset, restart, restore. Has any of that been tried?
It's possible the issue is with a specific app on the device interferring, a restore as new would confirm or deny that.
Also, as KiltedTim suggested, it could be a problem with the account on the carriers side.
On this hand set it did last 4 days unitl this problem came up.
I have done everything i can to get it fixed with out taking it to apple which you have to make an appointment 1 week in advanced in Australia.
I do believe it is a issue with an app i have. It was working fine untill i opened one of there apps, either Instragram or Instacam. These are my fav apps and i would still not like to get rid of them if possible.
I have deleted the apps of itunes and when i received this new handset i set it up as a whole new phone. But as i said above as new as i opened those apps 4 days later this happend right away.
I dont think it is a problem with the carrier.