Anybody with a 3GS will have to pay through the nose for the 4. The 3GS has only been out just shy of 12 months so they'll be an early termination fee whatever the pricing as shortest contract term is 18months.
For those who held onto their 3G, its a perfect opportunity to upgrade, but I suppose they've had to endure the sluggish-ness for so long!
Whats interesting at the moment is we have 3 carrier's selling the handset which will undoubtedly mean more competition. And more competition = price contest
That's why all the UK carrier's are holding back on pricing. Whereas in the US pricing is available because the handset is still exclusive to AT&T - therefore no competition.