Nokia, once the top smartphone manufacturer in the world, no longer cracks the top five. Sales of its Lumia line of phones have been growing, but not fast enough to offset massive drops in other products. In the company's most recent quarter, revenue fell 24% compared with the prior year. Its stock has been in decline for years. What happened? There were many causes for the downfall, but arrogance and a misguided focus on growing market share no matter the costs are two big ones. Like BlackBerry (BBRY), Nokia didn't take the iPhone's 2007 debut seriously. The U.S. market -- now home to the two leading smartphone operating systems in the world, Apple's (AAPL) iOS and Google's (GOOG) Android -- was merely an afterthought. And even as the world around them was changing, company execs clung to Symbian, Nokia's aging operating system, for far too long.

By the time Elop came on board in 2010, Nokia's reputation and market share were already tanking. "What has happened over the last couple of years is there has been a shift from a battle of devices to a war of ecosystems," Elop told an audience of mobile developers at a Qualcomm (QCOM) conference in 2011. Sure enough, soon after he took over the company, the CEO made a series of bold moves, most significantly hitching the company's fate to Microsoft's Windows operating system. The resulting offspring of that marriage is Nokia's Lumia line of phones. And while Elop's loyalties (and ability to lead the Finnish company) have been questioned, the Lumia smartphones are probably the best thing out of Espoo in a long time.

Elop's tenure at Nokia has been controversial, but unlike insiders he had the ability to divorce the company from Symbian and make a much-needed bet on a more viable operating system (albeit not a very popular one). It may have been too little, too late, and the "turnaround" Elop has subsequently led hasn't been flawless, to say the least. But this week's sale to Microsoft isn't surprising given the trajectory laid out in 2011. Investors are welcoming the deal, sending Nokia's share price up over 40% Tuesday morning.

"We view this positively for Nokia, as we believe the path for the Device & Services business was fraught with peril given competitive forces and its limited product acceptance," Maynard Um, a senior analyst with Wells Fargo, wrote in a report. "This sale and the buyout of the Nokia Siemens Network (NSN) joint venture all but completes the transformation of Nokia into a network infrastructure-focused business." (The remaining Nokia will consist of the company's telecom equipment business, mapping technologies and an IP licensing division). What's more, added Um, the sale puts more "financial muscle" behind the combined Microsoft-Nokia portfolio of products. That is, of course, if Microsoft plays its cards right.

The software giant doesn't have a good track record when it comes to hardware. Or acquisitions. But Elop's return into the fold could be helpful to the future of Nokia's handset line. Current Microsoft CEO Steve Ballmer recently announced he will be stepping down in the coming months, and many have weighed in on the list of potential successors. It's no surprise that Elop is now a top contender as well. The former insider knows the company well (he once ran its Office division). But after three years at Nokia, he also knows the handset manufacturing world much better than most Microsoft execs. As part of Microsoft's acquisition, Elop will step down as CEO of Nokia and take on the devices and services division at Microsoft, a big chunk of which will be made up of the former Nokia business. That means Elop may become the handset business' (and former Nokia employees') greatest hope. If he becomes CEO of Microsoft in the months to come, that may bode even better for the handset manufacturer formerly known as Nokia, painful as that admission may be to the Finns.