AT&T's (T) push into Mexico's wireless phone market seems to be gaining traction vs. incumbent America Movil (AMX), analysts say.

AT&T said it added 529,000 wireless subscribers in Mexico in Q1, with one-fourth the higher-spending postpaid customers who are billed monthly. Late Tuesday, AT&T reported that its Q1 operating loss was $251 million, amid network investments and subscriber acquisition costs.

"This is now the second consecutive quarter with 500,000 plus net adds, giving us confidence in the execution of the strategy abroad," said Amy Yong, a Macquarie analyst, in a report. "Profitability is also expected to improve by the second half of 2016. We expect free cash flow contribution could come as early as 2017."

AT&T and America Movil acquired more radio spectrum in a radio spectrum auction held by the Mexican government last quarter.

In the U.S., AT&T said it lost postpaid phone lines for the sixth consecutive quarter amid stiff competition from Verizon Communications (VZ), T-Mobile US (TMUS) and Sprint (S).

AT&T acquired Mexico's No. 3 wireless firm, Iusacell, as well as Nextel Mexico out of bankruptcy, for a combined $4.4 billion. It's spending over $3 billion to upgrade networks to 4G technology.

With the Q1 gain, AT&T has 9.2 million total wireless subscribers in Mexico.

AT&T's subscriber gains could accelerate after it finishes the 4G network upgrade, says Colby Synesael, an analyst at Cowen & Co.

America Movil, which sells wireless services under the Telcel brand in Mexico, holds nearly 68% of the market, with Telefonica (TEF) at 19% and AT&T at 13%. Controlled by Carlos Slim, America Movil is one of Latin America's two largest wireless services providers, along with Telefonica.