AT&T and T-Mobile have introduced a database that will track stolen cellphones and keep them from being used on the carriers' networks. All four major US carriers agreed to contribute to the database back in April; CTIA executive Chris Guttman-McCabe told IDG News that AT&T and T-Mobile have collaborated first because their GSM networks are essentially interchangeable.

"The goal is to not only protect the consumer by cancelling the service, but by ultimately protecting the consumer by drying up the after market for stolen phones."

It's not clear when Verizon and Sprint will introduce their own efforts, but all four carriers will operate a combined database by the end of November next year. The database records the unique IMEI number of each handset reported stolen — previously, carriers would simply block the SIM card to protect customers' accounts. Now that the database effort has begun in earnest, it should become a lot more difficult to use blacklisted devices on American networks.

Update: The CTIA has confirmed to us that all four major providers have their databases up and running. In a statement, CTIA president Steve Largent had the following to say:

"CTIA and its member companies have always been advocates for wireless users' safety, which is why we're pleased our members met the voluntary deadline to create databases that will prevent stolen smartphones from being reactivated.