Are one in three iPhones sold being unlocked?

Apple may have touted last week at MacWorld that it has sold nearly four million iPhones to date, but their numbers don't exactly match up with the number of iPhone activations by AT&T and their European partners: O2, Orange and T-Mobile.

AT&T this week revealed it ended the year with "just at or slightly under two million iPhone customers," while European operators are believed to have sold between 300,000 and 400,000 handsets - totaling around 2.4 million. This, with Apple's 3.7 million iPhones sold announcement, leaves 1.3 million of the devices unaccounted for, meaning either Apple is talking about shipped to store sales (and thus is facing a growing pile of unsold iPhones in stores) or that an awful lot of people have gone to the trouble of unlocking the devices to run them on different networks.