If you believe Apple, many of those missing phones were "unlocked" by their owners using unauthorized software or techniques, so that they can be used on carriers other than AT&T. Not all of the features of the iPhone would work if it's hacked in that way, and there's a serious danger that under some circumstances, software updates pushed out by Apple would permanently disable the phone. Still, lots of people do it, sometimes because they don't like AT&T, and sometimes to make a statement.
Apple is very clear: hacking the phone voids the warranty: "Apple strongly discourages users from installing unauthorized unlocking programs on your iPhone. Users who make unauthorized modifications to the software on their iPhone violate their iPhone software license agreement and void their warranty. The permanent inability to use an iPhone due to installing unlocking software is not covered under the iPhone's warranty."
If you believe Wall Street analysts, there may be other major contributing causes. Certainly, many phones may be sitting in inventory at authorized dealers, and even at gray-market dealers who bought them up and then weren't able to unload them fast enough.
In any case, the important message is that there aren't 3.75 million iPhones users out there. There are closer to two million. That's a big number, to be sure. But when only half the iPhones shipped are in use with the authorized carrier, that means that Apple's not making as much money from telecom fees, and that consumers haven't embraced it as much as the 3.75-million figure would suggest.
Perhaps those users are like me: Extremely interested in the iPhone, but not particularly interested in changing carriers. When the iPhone works with T-Mobile ï¿¼ without unlocking it using third-party hacks ï¿¼ then I'll be able to try changing a light bulb with it.
How many iPhones do you think it takes to change a light bulb?