Wirelessly posted (8700g)

I guess you have probably tried a hard reset (remove battery for 30+ seconds).

Have you tested in another location (so that you are on another tower)?

Are you running 4.2, or still running 4.1? Upgrading wouldn't hurt if you haven't done it already.

And call customer service if all else fails.

Maybe others have some ideas.

And out of curiosity, if you turn the radio off and back on again, will you get GPRS again?