I was wondering whether this is possible...

If I buy an O2 SIM card (pay as you go) and get the 10 per month bolt on which provides unlimited web browsing. Could I use this on the iPhone 3G when it is unlocked so that I would be able to use 3G (or EDGE) and I would pay the 10 every month allowing me to have iPhone with no contract but unlimited web browsing?

Also, does anyone know roughly when it will be unlocked?