The mobile-phone market in the U.S. appears to have peaked. The networks added just 200,000 postpaid subscribers and about 1 million no-contract customers in the first quarter, according to a report from consulting firm Chetan Sharma. Only two years ago, the Big 4 networks added 5 million subscribers in the comparable quarter.

Market leaders AT&T (NYSE:T) and Verizon (NYSE:VZ) continued to run away from the pack. On the next level, Sprint Nextel (NYSE:S) and T-Mobile USA (NASDAQ:TMUS) continued their long-standing negative trends.

All of this is fairly natural: The market has reached super-saturation, with more than 300 million mobile subscriptions. Not too shabby for a nation with 314 million citizens, including those too young, too old, or too Luddite to own a phone of their own. Growing at this point largely means stealing market share from somebody else. Ma Bell and Big Red keep leveraging their economies of scale to grow even more dominant, at the expense of smaller competitors.

But that doesn't mean the end of stronger business in the sector. Service revenues increased 14% year over year thanks to the shift toward higher-cost services. Mind you, smartphones now account for 85% of new handset sales and more than 50% of the overall market. It's only a matter of time before this segment, too, becomes saturated. But we're not there yet.

Once again, the big boys lead the way. Verizon and AT&T account for 70% of mobile sales but just 66% of subscribers, which points to higher revenues per subscriber. Breaking it down just a bit further, AT&T sells more iPhones than Verizon but fewer smartphones overall.

Consumers clearly feel that the largest networks are worth paying a premium for. That's why the lesser lights are consolidating at breakneck speeds.

Sprint is likely to buy data-networking partner Clearwire (UNKNOWN:CLWR.DL) in the near future, and the whole package will be swallowed by Japanese operator Softbank in a blockbuster $21.5 billion deal. T-Mobile just bought MetroPCS, and that combination might now become the Plan B choice for satellite broadcaster DISH Network, which wanted to buy both Sprint and Clearwire but lost both bids.

So the lower echelons of the industry are gaining international expertise and all kinds of capital infusions. If this wave of consolidation doesn't spark some innovation in the wireless market, I don't know what will. In the back half of 2013 and beyond, I expect a flurry of new devices, services, and rate plan options that you've never seen before.

It's an exciting time to be a wireless customer in America. Keep a close eye on the market and you'll find a lot to love as an investor, too. For stable operations with massive dividends, nothing beats Verizon and AT&T. For turnaround bets and a forced march into innovation, look closer at Sprint and T-Mobile.

Fool contributor Anders Bylund holds no position in any company mentioned. Check out Anders' bio and holdings, or follow him on Twitter and Google+.

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