I know the network has been down or still is however I regained my signal not long ago.
Anyway I got my signal back about 30 minutes ago whilst I had my sim in an older phone, when I put it back into my normal phone it says ''Your Sim Card Does Not Allow A Connection To This Network'' when i try and register on the o2 service.
I put my sim back in my old phone and still have network. I have done a battery pull and etc and still the same. Phone is a htc wildfire s if that helps?