Firstly, AT&T and T-Mobile are not merging. You may be thinking of the Sprint and T-Mobile merger that has been happening. AT&T attempted to acquire T-Mobile in 2011, but the deal was ultimately blocked by the U.S. Department of Justice due to concerns that it would harm competition in the wireless market.

On December 19, 2011, AT&T announced that it would permanently end its merger bid after a "thorough review of its options" which included a negotiation to sell a large portion of T-Mobile assets to Leap Wireless in attempts to alleviate concerns by the FCC regarding a monopoly, but to no avail.