Clearprop!!!
3G coverage is completly different to Network coverage. Even vodafone only have 60% of the UK covered by 3G because its an expensive network to install. I could post several forum posts about Vodafone poor coverage also, but as I said it deppends where you stay in the country etc. for you to say that O2's coverage is rubbish all the way through Scotland is non-sense I've been a BT Cellnet then O2 customer for well over 12years.
Telstar,
Are they the 3G one or the old one? I believe some countries have unlocked iPhones because the legislation in that country prevents companies from locking the phones for competition reasons. I believe France do it but I may be wrong.
If your looking for an iPhone, my advice would be get yourself a normal 2G iphone and pop a SIMO SIM card in it with the web bolt on added. No contract, cheap SIM Only SIM card. I must be honest, there isn't a huge difference between the 2G and 3G apart from network speeds and the A-GPS system (which I wouldn't use anyway, if you want a GPS system, buy a GPS system!)