Scale, spectrum and synergy--that's what AT&T, the nation's second largest wireless carrier, is hoping to get out of its purchase of T-Mobile USA, the fourth largest U.S. carrier. If the merger goes through, the combined firm would have 130 million subscribers and save as much as $3 billion annually, which would make the $39 billion deal well worth it. AT&T would be the undisputed boss of mobile, with control of the largest amount of network bandwidth, which is getting harder and more expensive to come by. That will be important in the years ahead as mobile data continues its exponential growth--up 132% in a year, according to Chetan Sharma Consulting. But the question consumers are asking is, Will it make my mobile-phone bills cheaper? The answer is no. Consolidation may create economies of scale for companies, but it rarely saves you money.