If you have AT&T and T-Mobile, it was easy for a thief to steal your phone and then pop the SIM out to resell it to someone else. Sprint and Verizon are more difficult, unless they are new LTE devices with a SIM, because they are provisioned through the carrier. Thankfully, that all changes now as these four major carriers turned on the joint database to track the IMEI numbers of cell phones, which is specific to the hardware and not the SIM card. Read the full story on zdnet.com