Thanks for all the replies! I have been on O2 for the past 10 years, and have only had signal problems with the iPhone 3G, my original iPhone (Classic, whatever) never had any problems.
I have had the 3G since launch here in the UK, and had about three outages that lasted a day each. I live in Bristol so I'm not in the sticks!!!! When it has gone down before I have not been able to do anything with the internet, so no FB, emails or weather updates etc, and nothing works to bring it back (usual restoring etc.), I just have to wait it out. I know I am not alone as when it has happened before both Apple and O2 forums have been full of people moaning.
Anyway, this morning must have been a short outage so all is good