Sarah Tew/CNET

Microsoft is once again going with a single carrier to launch its flagship smartphone.

The Redmond, Washington, company earlier Tuesday unveiled the Lumia 950 and Lumia 950 XL, which are positioned as the flagship smartphones using its Windows 10 software. When the Lumia 950 hit the US market in November, it will only be available through AT&T, according to a Microsoft executive.

"It's the best distribution for this family of devices," said Tuula Rytila, corporate vice president of marketing for phones and new devices, in an interview.

It marks a continuation of the strong relationship between AT&T and the devices team from Nokia, which Microsoft bought last year. But it also means customers who are on other US carriers such as Verizon Wireless won't be able to buy the smartphone (you can take an unlocked Lumia smartphone to T-Mobile). Microsoft believes it will get more of a focused promotional push of its devices through a single carrier.

AT&T confirmed it would be carrying the Lumia 950, but didn't mention the Lumia 950 XL.

Rytila said the Lumia smartphones would be broadly available in Europe.

Smartphone vendors typically strike exclusive agreements with carriers because they get marketing support and more shelf space at carrier stores. But they've gone out of style, with companies such as Apple, Samsung, HTC and LG pushing to get their phones broadly available through many carriers.

In this case, Microsoft said that its deal with AT&T is not exclusive to the carrier, and that the software titan was having discussions with other carriers both in the US and abroad about carrying both smartphones.

AT&T, which is the nation's second largest carrier, has a mixed track record of exclusive smartphones that got a promotional push. AT&T was also the home of the Amazon Fire Phone and the HTC First, also known as the Facebook phone, which were both exclusive devices that flopped. The carrier's biggest successful exclusive phone was Apple's iPhone.

Correction, 1:54 p.m. PT: The deal between AT&T and Microsoft for the Lumia 950 is not an exclusive one.