Of course, I am with T-Mobile.

I usually buy euro unlocked phones via ebay. Pop in the sim and am good to go. In the EU, phones must be unlockable so the phones will be here this fall.
The real reason to want to unlock them is to sell them overseas. The iPhone has all the GSM freqencies covered. Lot of money will be made selling them via the "black" market until aan official release in the fall in the EU. Elsewhere in the world, who knows what Apple has planned?