http://www.o2.co.uk/iphone/paymonthly -- existing customers pay £99/£159, get the new phone. Looks like I might even be able to downgrade my tariff to £30/month, though I'm not exactly sure I want to because if I was on a 75/200 tariff I might actually have to keep track of minutes.
Oh, goodness; the unlimited free WiFi, which at the moment is only through the not-very-prevalent Cloud, is going to include BT Openzone from 11 July. I've accidentally picked up BT Openzone hotspots hundreds of times since having the iPhone; this is very good news.