T-Mobile (TMUS 0.47%) has the worst mobile network ranking behind Verizon (VZ 0.88%), AT&T (T 1.30%), and Sprint (S), according to RootMetrics' Mobile Network Performance in the United States study.

Despite coming in last place among the four major players, the Un-carrier actually has a lot to be happy about. In just a year the company has raised its score from 71.5 to 82 -- a not-insubstantial jump.

T-Mobile has made gains, specifically in urban areas, according to the research firm:

T-Mobile's performance within metro areas was strong in multiple test categories, with improved data reliability and fast speeds. If you primarily use your smartphone in a major urban environment, T-Mobile remains a solid choice. Even though urban areas carry more weight in our results, T-Mobile currently lacks the broad coverage to excel in our National or State RootScore studies.

That's a nice positive step forward, but it still leaves the company with weak points in its coverage areas. But T-Mobile has found a unique way to address that problem and it might well remove any concerns many users had over its network and whether switching to the carrier, which generally offers better pricing than market leaders AT&T and Verizon, makes sense.

A cell tower in your house?
In addition to continuing to invest in its network (which all four major carriers continue to do), T-Mobile has decided to allow customers to shore up any weaknesses in their home network. The company has become the first U.S. wireless carrier to offer its users a free mini 4G LTE tower for their home. Called CellSpot, a customer simply needs to call the carrier or visit one of its retail stores to request the device, paying just a $25 deposit (and agreeing to return it undamaged).

The 4G LTE CellSpot Source: T-Mobile

"Think of it as your own 4G LTE mini-tower -- with low power settings for indoor use -- providing an average 3,000 sq. feet of glorious full-bar T-Mobile LTE coverage throughout your home, small business or virtually anywhere you need it," the company wrote in a press release.

When you say "cell tower," even adding the word mini in front of it brings people visions of those abnormally tall fake trees that stand out like Donald Trump at a Pitbull concert. This isn't that. The 4G LTE CellSpot measures 8.5 inches wide by 8.5 inches tall and is 1.3 inches thick. It's fully "plug-n-play," according to the company, which said you just have to hook it up to the Internet, plug it into the wall and "boom! You've got a clear, strong LTE signal covering 3,000 sq. feet on average."

Why is T-Mobile doing this?
The company noted that other carriers are using "small cells," but they are deploying them "where they think customers should get better coverage."  By letting the customers deploy the technology where they will actually use it, T-Mobile is creating an answer for people who might use its service but are wary because of weak coverage in their home or business location.

"The 4G LTE CellSpot supports up to 16 calls at one time; works with any 3G, 4G or LTE device compatible with T-Mobile's network, including those that can't use Wi-Fi calling; and can deliver 4G LTE even in places where cellular signals aren't available," says T-Mobile. The 4G LTE model joins an earlier CellSpot Router, which the company has given out more than a million of, and the 4G LTE CellSpot Signal Booster which amplifies T-Mobile's 3G, 4G and/or LTE signal throughout a home or business without an Internet connection.

Basically, T-Mobile is doing everything it can to ensure its customers have full bars at their home or office location.

Will this work?
T-Mobile has already improved its network significantly and doing this may further close the gap with AT&T, Verizon, and Sprint. It's not a replacement for continuing to upgrade its network, but it's a nice enhancement to one that has already gotten much closer to its rivals' performance.

By offering these devices for free, T-Mobile has given its customers an in-home or in-office network that rivals or exceeds any other carrier. That may not be quite enough to say it has a better network than Verizon and AT&T, but it further shrinks the once-large divide, which is getting close to becoming irrelevant (if it hasn't already).