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BARCELONA, Spain — Microsoft is setting itself up as the antiflagship phone maker, at least until Windows 10 comes out.

At the Mobile World Congress here on Monday, Microsoft for the first time showed off Windows 10 for phones and continued its evolving strategy of delivering low-cost Lumia devices that are attractive to emerging phone markets — and the growing prepaid phone market in the United States.

The Lumia 640 and Lumia 640 XL are brightly colored; can be upgraded to Windows 10 when that mobile operating system finally debuts; and although pricing may vary by carrier, they will start as low as 139 euros, or about $156, for a 3G version and €159 for a 4G LTE model. That translates to phones that are cheap or free with new contracts or on prepaid plans, or affordable enough to be bought outright. The Lumia 640 offers a five-inch display, while the Lumia 640 XL is, not surprisingly, much larger, with a 5.7-inch screen.

The Lumia 640 XL will be available starting in March, and the Lumia 640 comes out in April.

Manufacturers like Motorola and Microsoft have recently been eschewing high-end phones that are usually aimed at status-conscious buyers in the United States, in favor of creating devices that are affordable around the world. About one billion people are expected to be upgrading to smartphones in 2015 alone.

“We’re finding a lot of success,” said Stephen Elop, the executive vice president of the devices division at Microsoft. “Our Q2 results, in terms of the number of actual phones sold, was the largest quarter ever in the history of the Lumia line. And most of those sales were in the lower price tiers, those people who are buying not only in an AT&T or Verizon store but Walmart or Target.”

Microsoft said the Lumia 640 line represented few compromises: Its Qualcomm Snapdragon processor runs at 1.2 gigahertz; it has a high-definition display and a nine-megapixel camera; and it comes loaded with Microsoft services, like a one-year subscription to the personal edition of Office 365 (which can be extended to one computer and one tablet), an included terabyte of OneDrive storage and some free Skype calling.

At a show and in an industry dominated by the release of high-end, high-priced and high-powered phones like the flagship devices created by Apple and Samsung, it is the more accessible models that might find broader success. But as shoppers increasingly choose phones for the services that run on them, hardware with acceptable power and lots of included software might prove a winning strategy over time.

Microsoft also demonstrated some Windows 10 features, focusing primarily on how it keeps information, like search history and reminders, synced across devices and has a reading view for articles on mobile. Users familiar with, say, Google will obviously not find such features particularly groundbreaking, but they will be handy. For example, if you use Cortana to set a reminder on your PC, the reminder will automatically sync to your phone.

Mr. Elop said that the company would not snub the flagship forever and that it would debut high-end Lumia devices once Windows 10 was released this year.

At its news conference in Barcelona, Microsoft also showed off a new Bluetooth folding keyboard, usable with both iOS phones and tablets, Android devices and Windows tablets, as well as a new office suite for small to medium-size businesses, developed with AT&T.

“We also recognize that, particularly in developed markets, that flagship moment is really important,” Mr. Elop said. “We’re committed to the flagship, and you’ll see some beautiful devices later in the year.”

Mr. Elop declined to specify when Windows 10 might be released; the company has said only that it would be in 2015.