America Movil, the nation’s largest MVNO, lost around 3 million customers during the past 12 months. The operator reported fourth-quarter results showing a decline in its subscriber base from around 26 million customers in the fourth quarter of 2016 to around 23.1 million customers in the fourth quarter of 2017.

“We finished the year with 23.1 million subscribers—11.3% less than a year before—after net disconnections of 685 thousand Safelink subscribers in the quarter and net gains of 74 thousand clients in our other brands,” Mexico’s America Movil wrote in its brief fourth-quarter earnings report (PDF).

America Movil, backed by billionaire Carlos Slim, has long been a quiet player in the U.S. market through MVNO relationships with virtually all of the nation’s major wireless network operators. America Movil operates a number of prepaid brands in the United States including TracFone, Safelink, Straight Talk, Total Wireless and others.

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In its earnings report, America Movil hinted at some momentum in the market for some of its brands in the fourth quarter: “Other brands with higher ARPU such as StraightTalk and Total Wireless registered net gains in the period so the client mix resulted in an 11.9% increase in our blended ARPU,” the company wrote.

Nonetheless, America Movil indicated it faced a difficult holiday season. The company mentioned “aggressive competition” in the prepaid business as part of the reason its EBITDA declined a whopping 26.4% in the fourth quarter compared with the year-ago quarter.

America Movil’s comments add additional fuel to the notion that major U.S. wireless network operators like AT&T and Verizon are working to convert prepaid wireless customers into postpaid ones.

"Industry prepaid adds were at their lowest levels in nearly three years, thus we estimate total industry phone adds were up just 6% Y/Y, implying an unusually outsized prepaid to postpaid migration," the analysts at Cowen and Company wrote in a recent research note to investors. "Whether this dynamic will continue and what exactly drove it is unclear, although it could either be more attractive postpaid plans or the bullish macro environment."

While America Movil reported mostly shrinking metrics in its U.S. business, the company did post an increase in its average revenues per user, from $23 in the fourth quarter of 2016 to $24 in the fourth quarter of 2017. That rise likely reflects a growth in the number of smartphone users at America Movil versus feature phone users.

In its overall business—which spans Mexico and a number of other Latin American countries—America Movil reported its steepest loss in 16 years, as Reuters noted.