T-Mobile USA had its best year ever in 2014, adding 8.4 million customers and most likely stepping above Sprint as the third largest carrier in the U.S., but it might not be enough.

Deutsche Telekom—the owners of T-Mobile USA—have warned that unless the U.S. carrier is sold it will still go into the black, despite the huge push in 2014.

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Timotheus Höttges confirmed T-Mobile USA does not have the funding to continue operations, and the "Un-Carrier" deals CEO John Legere is pushing in the U.S. remove lucrative profits from the company's portfolio.

T-Mobile USA is still on an operating profit, but when the carrier needs $4 to $6 billion in spectrum investments, it will not be able to salvage that much money and compete with AT&T and Verizon Wireless, according to Höttges.

The previous rumor claimed Sprint would acquire T-Mobile USA with cash from Japanese carrier (and owner) SoftBank, however this deal appears to have fallen through with the new CEO Marcelo Claure taking over operations.

AT&T and Verizon Wireless may be interested in picking up T-Mobile's near 60 million subscribers, but the profit margins are lower on T-Mobile contracts and it is not certain these customers will move over to their new owners.

There are a few potential buyers, including Google who wants its own wireless network to go alongside Google FIber. Google has over $50 billion in the bank for acquisitions, meaning it could go toe-to-toe with Verizon and AT&T.

Amazon and Asian business magnet Li Ka-shing—owner of Hutchison Whampoa—might also be interested in a U.S. wireless service, especially one with large brand recognition and an excellent 2014.

However, no company has openly looked towards an acquisition, possible due to some unforeseen factors T-Mobile USA does not want to share. It is not clear how much an acquisition of T-Mobile USA would cost, but Deutsche Telekom looks anxious to remove the subsidiary by any means.

TagsTim Höttges, Deutsche Telekom, T-Mobile USA, U.S. carriers