Elop was named executive vice president of the tech giant’s devices division earlier this week, as part of a handful of other management changes. Wednesday morning in San Francisco, he took the stage at Microsoft’s Build developers conference to announce three new Lumia phones: The 930, 630, and 635. (Unlike its just-announced, slickly-named personal digital assistant, Cortana, Microsoft is sticking to good old numbers for its phones.)

The Redmond-based tech company is expected to close its $7.2 billion acquisition of Nokia’s devices business later this month. Elop started off his keynote at Build by saying that he and the rest of the employee base at Nokia will be joining Microsoft “in a few days.”

“Together, we can bring people an amazing family of devices, of services, of applications,” Elop told the crowd.

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But whether apart or together, both Microsoft and Nokia have yet to prove they can gain mass appeal for their mobile products. Microsoft’s Windows Phone operating system for mobile devices is shadowed by the duopoly of Apple (AAPL) and Google (GOOG) . And Nokia, once the top phonemaker in the world, has never recovered from its massive decline following the iPhone’s launch in 2007. (Even with its steady lineup of Lumia phones, in late January Nokia posted annual results showing sales had slumped 29% over the year.)

Still, Elop and Microsoft are convinced they’ve got winners on their hands. The new crop of Lumia phones, available later this summer, will run on the updated Windows Phone 8.1 operating system. That means they will include a notification center that shows all new messages and updates in one screen, new personalization options and, yes, the aforementioned Cortana personal assistant (a distant cousin of Apple’s Siri?). The Lumia 930 also comes with a 20-megapixel PureView camera and Microsoft services like OneDrive and MS Office. The 630 and 635 are both lower-end phones; they retail for less than $200, while the 930 will cost about $600. All three phones come in five new colors: bright orange, bright green, bright yellow, black, and white. (Did I mention they’re bright?)

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Despite some success, the Lumia phones did not save Nokia. So will they save Microsoft? Of course, the tech behemoth isn’t in need of the same kind of life support Nokia needed, and it’s got a much more diversified and lucrative current revenue stream. But the Lumia phones, like many other Microsoft products, need to not only attract consumers but also developers — the coders and companies that churn out bite-sized mobile apps for consumers to download and use on the smartphones. That’s a tall order for Elop, who will now be tasked with overseeing all Microsoft devices.

New Microsoft CEO Satya Nadella — who happens to be Elop’s new boss — addressed this question head-on at this week’s Build conference. “You want to build for Windows because we’re going to innovate with a challenger mindset,” Nadella told the audience. Microsoft, he added, is no longer the incumbent. At least in mobile, he’s absolutely right.