T-Mobile will let you use your phone in Canada and Mexico without a roaming fee

T-Mobile is opening up the borders to Mexico and Canada for its subscribers.

The fourth-largest wireless carrier in the US on Thursday said it would allow customers use their smartphones -- to make calls, send text messages and browse the mobile Web -- in both countries without any roaming charges. They can also call Canadian and Mexican numbers from the US without incurring any fees. The program kicks off on July 15.

The move is part of T-Mobile's broader "Uncarrier Amped" campaign, just one of the many ways the four national carriers have tinkered with coverage plans, customer promotions and network upgrades to get a leg up on rivals.

Last month, for instance, T-Mobile introduced a plan that allows customers to upgrade their smartphones up to three times a year, a refinement of its Jump upgrade program, which previously allowed you to upgrade after 12 months, but required a $10-a-month fee.

Meanwhile, No. 3 Sprint has gotten more aggressive with a new marketing campaign and as larger rivals AT&T and Verizon Wireless have upped their own efforts, putting the wireless market in a state of flux. But T-Mobile's incentives have paid off: the carrier earlier Thursday said it added 2.1 million net new customers in the second quarter.

T-Mobile's latest program, dubbed "Mobile Without Borders," is an enhancement of its previous offer of free unlimited international data and text messages. That plan allowed you to use data, but it was limited to a slower 2G connection.

The new move gives customer access to the fastest possible connection in both countries. T-Mobile partnered with two carriers in Mexico and six carriers in Canada for full roaming coverage. Customers will have the same amount of high-speed data they have under their usual plan.

"Even if Donald Trump wants to put a wall up [on the Mexican border], the wireless coverage will work seamlessly," T-Mobile CEO John Legere quipped on a conference call.

Legere added that the alliance of carriers that has been stitched together represents "a sign of the future."

"International roaming and calling has been a significant revenue generator for all carriers, but T-Mobile is ushering in a new paradigm," said Lynnette Luna, an analyst at Current Analysis.

The "Mobile Without Borders" initiative comes as AT&T is preparing to open up access to Mexico for its own customers. The nation's second-largest wireless carrier acquired Mexican carrier Iusacell for $2.5 billion and Nextel Mexico for $1.875 billion, and envisions a single seamless network running throughout the two countries.

AT&T offers unlimited calls to Mexico as part of its Word Connect Value plan, which costs $5 a month.

An AT&T spokeswoman wasn't immediately available to comment on T-Mobile's new plan.

The free calls to Mexico and Canada represent a boon to T-Mobile customers. A majority of international T-Mobile calling minutes -- 59 percent -- go to those two countries, according to a spokesman.

"It's a huge impact for our customers," Legere said.

For some T-Mobile customers, there are a few wrinkles. Existing customers will have to check a box in their plan to add the feature. Anyone on a promotional program, such as an older unlimited plan or the bonus 2.5-gigabyte plan, will have to switch to a new program to take advantage of the new deal. If they don't want to switch, they can add the feature to their account for $10 a month.

Another requirement: T-Mobile customers have to spend more than half their time in the US to qualify for the free access. In other words, someone from Mexico or Canada can't sign up for T-Mobile service and move back home.

T-Mobile customers in the two countries won't be able to access to the extra data on its Data Stash program, which is the unused data from previous months that has been rolled over into the current tally. The carrier is working on making it accessible, a spokesman said.

While the program comes at a cost in the form of roaming fees it must pay to its partners, T-Mobile hopes it will bolster customer loyalty and convince customers who tend to make calls or do business in either country to take a second look at the carrier.

Updated at 6:58 a.m. PT: To include comments from the conference call.