haha.  I was in London with my iphone 4 last month (AT&T), with a $50 international data plan, and by the end of the FIRST day I got a text saying I had exceeded my data plan and to put the phone on airplane mode immediately.  Fortunately I had a BlackBerry with me and switched pronto.  The bill was $800!!!  Eeek!  Fortunately the bill has been adjusted.  Next time I'm going with my N1 and will pick up a local sim @ Heathrow.
I think Phil will have a massive bill :O