Wireless companies are going to start a blacklist for stolen phones. This is a long overdue move. It should have happened years ago. The downside to smart phones like the iPhone having a high resale value is that they have a high resale value. By that I mean they are targets for thieves.
Some, notably Sprint and certain wireless companies in other countries already have such blacklists. A search on ebay for “bad esn” returns quite a few phones. It’s virtually a guarantee these are all stolen phones. Some are sold for parts, some are taken to other wireless providers. Stay away from any phone marked as such if buying used or buy new. I know lots of developers buy older model new phones on eBay, and some buy used. Avoid the “bad ESN” listings so you don’t support this.
Hopefully the next step will be cooperating with overseas partners for a global blacklist. It shouldn’t be terribly difficult to accomplish. That would even further reduce the value of a stolen phone to being worth much more than it’s parts.