U.S. cable operators until quite recently found themselves facing a situation similar to what AT&T now appears to face in its effort to acquire T-Mobile USA. Basically, the Federal Communiations Commission ruled that no single U.S. cable operator could serve more than 30 percent of all U.S. cable TV subscribers. That rule was overturned, but the point is that there always is, in every mature market, a point beyond which regulators will not let market concentration proceed any further, at least for the few leaders of any market.
So the question is whether the U.S. mobile market has reached that important stage of development.
http://knowledge.wharton.upenn.edu/article.cfm?articleid=2334
