* Unveils service in Mexico, Canada
* Q2 net customer adds 2.1 mln, up from 1.5 mln a year earlier
* Q2 postpaid churn falls to 1.3 pct from 1.5 pct a year earlier (Adds executive quotes, background, updates stock price)
By Anya George Tharakan and Malathi Nayak
July 9 (Reuters) - T-Mobile US Inc said on Thursday that aggressive pricing helped boost its net customer additions in the second quarter by 41 percent over a year ago to 2.1 million, and also offered free calls to and from Mexico and Canada.
The No. 4 U.S. wireless carrier unveiled its "Mobile without Borders" plan, which includes calling, texting and high-speed data services at no extra cost for U.S customers on its "Simple Choice" unlimited service plan traveling in Mexico and Canada.
The plan builds on its previous roaming service that included free international 2G data and texting with call charges of 20 cents per minute.
Shares of T-Mobile, of which Deutsche Telekom owns 66 percent, rose 0.6 percent to $38.72 in afternoon trade.
The move is aimed at helping T-Mobile compete better with AT&T Inc, the second-largest U.S. wireless carrier, which bought Mexico's No.3 and No.4 wireless carriers Iusacell and Nextel Mexico this year.
T-Mobile will work with two leading Mexican wireless providers to offer wireless service without roaming costs to its U.S. customers, executives said on a media call without providing partner names or financial terms.
The company, which calls itself the "Un-carrier," has revamped its pricing plans, eliminated service contracts and launched aggressive marketing campaigns to help turn around years of subscriber losses.
T-Mobile said the rate at which users switched to other networks, also known as postpaid churn, fell to 1.3 percent in the quarter from 1.5 percent a year earlier.
The company also said its T-Mobile branded postpaid phone net additions, or new customers who pay on a monthly basis, grew 31 percent form a year ago to 760,000 in the second quarter.
"T-Mobile continues to draw customers away from peers - which should provide ongoing support for the company's sector-leading revenues growth," Evercore ISI analysts said in a note.
T-Mobile's net customer additions exceeded expectations of analysts at Evercore by 114 percent and estimates of Jefferies analysts by 84 percent.
T-Mobile is scheduled to report second-quarter results on July 30.
Investors are keeping a close watch on T-Mobile's subscriber numbers, now up to 58.9 million for the quarter ended June 30, to see if it will overtake No. 3 U.S. carrier Sprint Corp, which finished the first quarter with 57.1 million subscribers.
"We won't know for sure until (Sprint) releases" subscriber numbers, T-Mobile's chief marketing officer Andrew Sherrard said in an interview. "It's our ninth consecutive quarter with over a million net subscriber gains." (Additional reporting by Abhirup Roy in Bengaluru; Editing by Meredith Mazzilli)