Reading the entries here, I'm surprised that nobody mentioned the device IMEI. As far as I am concerned, the number one thing that Apple could do to help with the theft problem is to remove the economic benefit in the first place. People steal these phones because they can unlock them and sell them on ebay, or because they can wipe them and sell them on craig's list, and the buyer can roll right in to their local AT & T store and activate the phone without any questions asked. That's unconscionable.
First, it should not be possible for a crook to alter the IMEI of the device.
Second, if Apple really cares about this issue, they should lean on their carrier partners to NOT ACTIVATE phones that have been reported stolen. I recently had my iPhone 4 stolen, and I immediately reported it on the AT&T web site. AT&T knows the device IMEI, and there is no reason at all that they cannot prevent someone else from activating that device on their network; there is simply an unwillingness to do so.
Lock screens, auto wipe, find my phone... all of that stuff represents effort in the wrong direction because all of it is easily defeated. Crooks turn off the devices the second they pinch them, and then they wipe or unlock them, sell them, and enjoy the money. The real solution is to remove the incentive; if they know they won't be able to sell the device because it can't be activated, then they won't be motivated to steal the device in the first place.
There isn't a will to address this beyond a token level, I think, because a stollen iPhone is more revenue for everyone concerned. A) a stollen iPhone is a new activation for the carrier. What could be better - someone steals YOUR iPhone and then they go and activate it on a line of service. So now the carrier gets to bill you for service you aren't getting and they get another subscriber as well. Awesome! Even if the phone goes to someone who is just upgrading from a previous model, the carrier still gets to rope YOU into another few years of contract through their anemic device replacement policy. It's a win-win for the crook and the carrier. B) A stolen iPhone is another sale for Apple, because they know you are going to want to replace the hardware. So Apple benefits from the theft, too, because they just scored another device sale.
The whole thing stinks and I wish Apple would step back and think about this from the perspective of removing the incentive.