The whole of Europe is completely sold out of iPhones latest 3G variant. New stocks are also not expected to arrive before October which would mean that those who already got theirs would probably be able to demand a decent premium now that the unlocks are out. The 3G iPhone is still available sporadically around the United States with Apple releasing just enough stock daily to keep up interest.
AT&T stores are apparently without iPhone 3G inventory and this could last until August. Given that the iPhone notched up a million sales so quickly (which is something Apple already expected) its surprising that they were not already prepared for this situation before hand.
There were rumours even prior to launch that Apple had realised the potential of the handset and ordered its suppliers to boost their production levels in order to not disappoint thousands of early adopters. It does seem unlikely though that Apple would be reducing the supply of the iPhone on purpose, something that Nintendo have been accused of with their Wii console in order to keep up consumer interest.