Shares of the Bellevue, Wash., company at last check were up 6.3% to $124.62. The stock on Friday has traded up as much as 8.3%, above $127. That's a 52-week high, double the 52-week low of $63.50, set in mid-March.
T-Mobile posted earnings of $1.25 billion, or $1 a share, compared with $870 million, or $1 a share, in the year-earlier period.
Revenue increased 75% to $19.27 billion from $11.06 billion.
A survey of analysts polled by FactSet expected earnings of 46 cents a share on sales of $18.3 billion.
The company added 2.03 million subscribers in the third quarter. Of them, 1.98 million were postpaid customers, which generally are more valuable to the telecom-service providers than prepaid customers because they're less likely to switch to rival providers.
"Customers are choosing T-Mobile in record numbers," Chief Executive Mike Sievert said in a statement. He added: "We’re consistently and profitably outpacing the competition – and we’re just getting started.”
The company also cited faster-than-expected cost savings from its Sprint Corp. merger, which was completed earlier this year.
T-Mobile doubled its forecast for Sprint merger synergies and now expects $1.2 billion in cost and revenue benefits this year.
T-Mobile also raised its outlook for the second half, expecting higher adjusted Ebitda of $13.6 billion to $13.7 billion, up from the $12.6 billion to $12.7 billion it projected earlier.