T-Mobile is making the case that it's already the nation's third-largest wireless carrier by subscriber base.

Josh Miller/CNET

The crux of T-Mobile's argument lies in a line in Sprint's financial filings with the Securities Exchange Commission that counts 1.7 million customers through resale partners that have been inactive "for at least six months." T-Mobile CEO John Legere believes those customers shouldn't be counted, and suggested Sprint meddled with the numbers to put it on top.

Sprint, however, maintained that it has used this accounting method for years, following a policy to not remove a customer from its records until its resale partner officially notifies the company. The company declined to comment further on T-Mobile's comments.

Troy Thomas/Sprint

That there's even a debate shows how statistically close the two carriers were to end the year, a testament to the progress T-Mobile has made over the past two years and, conversely, the struggles that Sprint has dealt with. Sprint officially ended the quarter with 55.9 million customers, while T-Mobile ended up with a little more than 55 million.

Legere had previously projected passing Sprint by the end of the year. In his own way, he's keeping to his word.

There's little at stake in this debate beyond bragging rights, and it may end up being a footnote in the ongoing wireless wars. Given the different trajectories at T-Mobile and Sprint, T-Mobile will almost certainly surpass its rival.

"We expect to surpass them, shenanigans included," said Chief Operating Officer Mike Sievert.

T-Mobile earlier Thursday reported fourth-quarter results, which included a surprisingly strong profit and the addition of 2.3 million customers and 1.3 million customers who pay at the end of the month, also known as post-paid customers.

Sprint added 900,000 net new customers, but only 30,000 post-paid subscribers, seen in the industry as the most valuable segment of the market.