Hi, I've tried everything (the problem started this morning). I've taken the battery out and done a hard reset, I've gone to Advanced Options > Host Routing Table > Register and done that, but nothing seems to help. I don't get email or internet access. Mobile network is fine (O2), so I can make calls and send SMS etc. Please help.
Sometimes you have to go to Options > Advanced Options > Host Routing Table and use the Menu key to select "Register". Otherwise, do what Dubdub said and ring up o2.