(Reuters) -T-Mobile said on Thursday it added 1 million wireless subscribers who pay a monthly bill in the third quarter that also topped estimates and raised its annual forecast, powered by iPhone upgrades and premium plans that drew users from rivals.

Shares slipped 1.5% premarket after the company increased its annual capital expense forecast by $500 million to about $10 billion.

Device upgrade cycles typically raise costs for telecom operators, as they must purchase handsets and offer them at a discount to attract or retain customers.

For U.S. wireless carriers, the third quarter is seasonally crucial as Apple's ( AAPL ) latest iPhone models typically trigger a spike in upgrades and new subscriptions.

T-Mobile's premium plans have helped it win a larger share of switching customers in what analysts have described as a "musical chairs" environment.

When customers shop for new devices, "it creates a tremendous opportunity for us to earn switching business from our competitors. And I think in Q3 that's exactly what you saw," Mike Katz, president of marketing, strategy and products, T-Mobile, told Reuters.

The monthly bill paying wireless subscriber additions marked T-Mobile's highest in the third quarter in more than a decade. Analysts had expected 844,900 additions, according to FactSet.

The company is also drawing customers with its T-Satellite plan, which allows users to connect in remote or rural areas where traditional wireless service is limited.

A vast majority of users that are opting for the direct-to-cell service are getting it through T-Mobile's "Experience Beyond" plan which offers it at no extra cost, Katz said.

T-Satellite, which commercially launched in July with access limited to SMS texting, MMS, picture messaging and short audio clips, now supports widely used apps, including WhatsApp, Google Maps and X.

The carrier now expects to add between 7.2 million and 7.4 million total postpaid net customers in 2025, compared with its prior projection of 6.1 million to 6.4 million additions.

Total revenue for the third quarter came in at $21.96 billion, compared with expectations for $21.92 billion, according to data compiled by LSEG.

(Reporting by Harshita Mary Varghese in Bengaluru; Editing by Sriraj Kalluvila)