Last April AT&T announced that it will be unveiling a service which enables blockage of stolen iPhone to use it’s network. Once a customer looses his iPhone the customer can contact AT&T to block that iPhone. Once an iPhone is blocked it cannot use AT&T network at all. The verge reported that it found a leaked memo screenshot of AT&T claiming the launch of this service by 10th July 2012.
In April the four major carriers in the US AT&T, Verizon, T-Mobile and Sprint announced a common database of stolen phone to be built as requested by FCC. This might well be the beginning of that proposal.
AT&T also mentioned in the memo that only the person who requests for a block of iPhone can unblock it again. Hope this decreases the number of iPhone being stolen.