Shares of Sprint (NYSE:S) nearly doubled in 2013. The third-largest American telecom treated investors to an 89% gain, far ahead of the S&P 500 index's 32% return. Sprint entered 2013 as a perennially troubled and financially unsound business, but walks into 2014 with Clearwire's spectrum under its belt, and $5 billion of Softbank 's money in the pocket.

How will the revamped Sprint measure up in 2014?

The integration with Japanese peer Softbank has been fairly hands-off so far. According to Sprint CFO Joe Euteneuer, it amounts to weekly video conference meetings between Japan and Kansas, where Sprint and Softbank leaders check out "what's going on in each of our businesses and how do we learn from each other." Monthly face-to-face meetings focus on best practices, and how to drive synergies through the combined companies' economies of scale.

Wall Street analysts see Sprint reporting an adjusted net loss of $0.48 per share in 2014. That would be an improvement from the $0.94 net loss per share estimated for 2013, and the $1.41 loss per share reported in 2012. On the top line, revenues are expected to stay almost flat compared to 2013, making a two-year sales-growth trend of 1% or less.

The cash infusion from Softbank was extremely timely, because Sprint started burning cash last year. CEO Dan Hesse will have to turn this from upside down in 2014, when the current wave of expensive network upgrades runs to completion.

Sprint plans to complete its Network Vision project in 2014. That means installing 4G LTE service on three distinct network bands nationwide, then leveraging the newly installed capacity to steal customers from AT&T and Verizon. Following the Sprint-Clearwire merger, Sprint holds more spectrum bandwidth than the two larger networks combined, and now the challenge is to actually create a high-speed business advantage from these rich spectrum reserves.

S Revenue (TTM) Chart

S Revenue (TTM) data by YCharts

Sprint might not be done with big-ticket mergers quite yet. Following the game-changing combinations with Softbank and Clearwire in 2013, rumor has it that Sprint might send an official $20 billion merger bid to T-Mobile (NASDAQ:TMUS) any day now. If this deal comes to pass, the new T-Sprint would play in the same ballpark as longtime market leaders Verizon (NYSE:VZ) and AT&T (NYSE:T), each of which sport about 100 million wireless customers. Sprint's 54 million subscribers, and T-Mobile's 45 million, add up to a third megamajor in the U.S. market.

Look for more merger rumblings in the days ahead, and keep an eye on Sprint's rapidly improving network quality and connection speeds. Sprint is definitely giving Verizon and AT&T something to worry about -- with or without a T-Mobile merger.