Despite a slow start, Windows Phone 7 and Windows Mobile's combined market share will overtake Apple's iOS within five years. That's one of the conclusions from IDC's Worldwide Quarterly Mobile Phone Tracker report, released Wednesday.

The study indicated that Phone 7's upward climb will be assisted by Nokia's continuing strength in emerging markets. By 2016, the research firm expects the mobile platform to squeak by Apple's market share, with 19.2 percent for Microsoft and 19 percent for Apple. That compares with 2012 market share of 5.2 percent for Windows Phone 7/Windows Mobile and 20.5 percent for iOS.

Android, RIM

Both now and in 2016, IDC expects Android to remain the No. 1 smartphone operating system. It currently has 61 percent market share, and IDC projects it to have 52.9 percent in five years.

The only other specified platform that IDC ranks is Research In Motion's BlackBerry OS, which now has 6 percent and is projected to remain about the same, about 5.9 percent, by 2016.

IDC notes that both Windows Phone and BlackBerry are in the process of a major transition. Windows Phone is still working to gain more than a foothold, and could be propelled -- or hindered -- by tie-ins with the coming release of Microsoft's Windows 8 OS. RIM is expected to release its new BlackBerry 10 OS later this year, which will determine if the phone maker has a big or a small future.

Keeping the same market share while the size of the market increases could be seen as a victory of sorts for the beleaguered Canada-based phone maker. As with Windows Phone, IDC sees RIM being bolstered by its position in emerging markets, where, it notes, "users are looking for affordable messaging devices."

One OS that has long populated -- and once dominated -- such lists, but which is only now mentioned in passing, is Symbian. It helped Nokia attain the position it currently has, but Nokia's switch to Windows Phone has led to a sharp drop in Symbian's market share.

Microsoft's Investment

IDC also projects the worldwide mobile phone market as growing at a bit more than 4 percent in 2012, which is the lowest annual growth rate in three years.

The reasons, according to the study, include a sharp decline in the feature phone market coupled with an ongoing sluggishness in the world's economy. Feature phone shipments are expected to drop by about 10 percent this year as the transition from feature phones to smartphones continues gradually but steadily.

In spite of their slow decline, feature phones still rule, constituting an estimated 61.6 percent of all mobile phones in 2012. But in actual units shipped, that still means about 1.8 billion mobile phones this year, and about 2.3 billion in 2016.

We asked Ross Rubin, executive director for Connected Intelligence at the NPD Group, if the optimism about Windows Phone was warranted.

He said it could be, and that it was based on two main factors. First, "Microsoft continues to invest heavily in the platform," he said, adding that all the projected three top ecosystems -- Android, iOS, and Windows -- "either have key relationships with handset makers or they themselves make the devices."

The other factor in Windows favor, he said, is the "belief that Nokia will be able to count on a significant amount of strong global presence," such as in emerging markets.