During the past year, T-Mobile (NASDAQ:TMUS) has fought tooth and nail to remake itself into a competitive mobile provider, and with possible wireless spectrum deals on the horizon, the company is about to dig its trenches even deeper.

If you build it, they will stay
Earlier this week T-Mobile announced that it's holding a second offering to raise about $2 billion to buy additional wireless network spectrum. T-Mobile will sell about 66 million shares at $25 per share, with an option for underwriters to purchase an additional 6 million shares. Wireless carriers often look for additional spectrum in order to grow their networks so they can handle additional customer data usage.

In an SEC filing this week, T-Mobile said: "Although we do not intend to participate in the FCC's upcoming auction of 1900 MHz PCS H block spectrum, we are currently considering an acquisition of spectrum from a private party. If we reach agreement to acquire such spectrum, we anticipate that a portion of the net proceeds of this offering will be used to finance such acquisition."

T-Mobile will use some, possibly most, of the money from the second offering to buy up spectrum from a private party. So far, the company hasn't disclosed any details about how much spectrum it will purchase, or from whom it's buying it from.

Why does more spectrum matter to T-Mobile? Because the company is making good progress in customer growth, and it needs to hang on to it.

The un-carrier underdog
T-Mobile has had a solid two quarters of customer growth, adding 1.3 million net postpaid branded subscriptions. In case you're not familiar with that jargon, net postpaid customers are the ones who pay a regular monthly price for their service. T-Mobile doesn't have contracts, but postpaid customers typically bring in more money for the company than prepaid customers. Branded subscriptions simply mean the subscribers are actual T-Mobile customers instead of customers of T-Mobile's partner, Metro PCS.

For comparisons' sake, AT&T added about 1 million net subscribers this past quarter. That's a lot more subscriber adds than T-Mobile, but remember that AT&T is at the top of the food chain.

T-Mobile has been able to grow its customer base by offering users clear pricing and low monthly costs. But wooing subscribers is only part of the battle; making them stick around with a fast and extensive data network is the other part. T-Mobile has already expanded its 4G LTE network to 254 cities and 203 million people, but that falls far short of its competitors. AT&T's 4G coverage is available to 288 million people, and its LTE is available in 459 markets, while Verizon Communications' wireless division has more than 500 cities on 4G LTE, and covers about 95% of the U.S. population. Acquiring additional spectrum will allow T-Mobile to beef up its network and help the company ensure all of its newly gained customers actually stick around.

Fool contributor Chris Neiger has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.