Imagine a world where Windows Phone is more popular than Apple’s iPhone.

That may just sound like Steve Ballmer’s fantasy, but a recent Gartner report claims that it may very well happen by 2015, thanks to a boost from Nokia as Microsoft’s mobile partner.

The prediction is far from crazy: I’ve argued in the past that Microsoft will doggedly fight to reclaim its mobile relevance, and it could very well achieve that with Nokia being the premiere Windows Phone 7 device maker.

The firm assumes that Nokia will begin banking heavily on Windows Phone next year, which will help notch it up to the third most popular smartphone platform in the world by the end of 2013. Come 2014, Windows Phone and the iPhone will be going head-to-head, and Microsoft will come out on top in 2015 with 19.5 percent market share compared to Apple’s 17.2 percent, Gartner predicts.

But I don’t think Apple should be shaking in its boots yet.

Gartner makes some massive assumptions to reach its figures — including the fact that Apple will prioritize margins and won’t try to fight for market share with low-cost and mid-range smartphones. Apple has arguably already proven that assumption false by selling older hardware for low prices, like the $50 (with contract) iPhone 3G S.

Gartner’s prediction that Nokia will focus mostly on Windows Phone 7 devices by next year seems similarly weak. It “would be an organizational miracle,” according to Horace Dediu at Asymco (who also chalked Gartner’s projections up to “divine inspiration”).

Not surprisingly, the big winner in Gartner’s analysis is Android, which it predicts will have 48.8 percent of smartphone market share by 2015. But since predictions of Android’s dominance in the next few years are a dime a dozen, that didn’t seem nearly as interesting as its Windows Phone estimates.

VB Mobile SummitCalling all mobile executives: This April 25-26, VentureBeat is hosting its inaugural VentureBeat Mobile Summit, where we’ll debate the five key business and policy challenges facing the mobile industry today. Participants will develop concrete, actionable solutions that will shape the future of the mobile industry. The invitation-only event, located at the scenic and relaxing Cavallo Point Resort in Sausalito, Calif., is limited to 180 mobile executives, investors and policymakers. We’ve pretty much finalized the invite list, but have a few spots left. Request an invitation.