The market for used iPhones is fraught with risk, because you may end up paying hundreds of dollars for a locked off device, or worse -- one that appears legit but can't make calls. However, Apple has just revealed an iCloud tool that lets you check a device's activation lock status. All you'll need is the iPhone's IMEI or serial number, and if you're the rightful owner, you'll get info on how to disable any activation locks before selling. Meanwhile, buyers will be shown how to remove the previous account (with the seller's permission). The tool will be particularly useful at sussing out "doulCi" devices, which bypass iCloud to enable activation but won't actually connect to a cell network. That'll prevent you from being fooled by a stolen or lost iPhone that appears to work, but is effectively... an iPod.