The wireless carrier's Open World plan will also charge five cents per minute for calls to Latin America, the Dominican Republic and over 180 countries around the world.
The new international feature will automatically tack on to select plans starting in August.
The $1.875 billion deal follows its acquisition of Iusacell and bid to expand its presence in Mexico.
AT&T names veteran executive Thaddeus Arroyo CEO of the new Mexico City-based leadership team for Iusacell.
The company's promotion will allow people to call Mexico all they want, as well as use their devices in the country, free of charge until 2016.
The offer is targeted at rival AT&T, which just closed its acquisition of DirecTV and began offering its own bundles of discounted wireless and satellite TV services.
T-Mobile's chief operating officer, Mike Sievert, visits CNET to talk about its expanded calling plan, competition and whether Dish would make a good employer.
You'll also be able to call Canadian and Mexican numbers from the US at no extra charge. It's the latest in a series of programs as T-Mobile jockeys for better position.
The car-hailing service's ban in New Delhi has been revoked, but it will be hit with levies and regulations in Mexico City.
The e-commerce company added physical goods to its Mexico website, including baby products, DVDs, tools and appliances.