Call Forwarding using a UK O2 network G3 iPhone

I have a G3 iPhone, but having moved job and house I find that the O2 signal where I live and work is abominable and it is very rare that I can get to make or receive a decent call from my iPhone. O2 don't really seem interested, just telling me that their coverage maps shows reasonable coverage. Yeah !

I can't get out of the contract, but do want to make sure that I can at least receive calls from my iPhone when people are calling. So, I want to forward calls from my iPhone to my home / office/ other number.

How do I activate call forwarding from a UK O2 network G3 iPhone. I've looked and looked and looked and can't seem to find anything that let me do it.

Advice from UK people who have an iPhone on an O2 contract - (the only network provider you can get for iPhone in the UK - what happened to competition ? - oh, the French made sure there wasn't a monopoly market, so why couldn't we ?!) - would be appreciated.

Thanks

Chris