Market research firm IDC estimates smartphone shipments will grow 38.8 percent this year, hitting 686 million units in 2012. But while Android and iOS lead the smartphone pack now, in the long term the company is predicting Android and iOS’ market share will decline, largely at the expense of Windows Phone.

According the company’s latest study, the combination of falling prices on devices and data plans, and high subsidies from carriers is boosting current smartphone demand. However, IDC expects smartphone market share growth will be less agressive this year, as the rate at which consumers switch from feature phones to smartphones begins to slow.

“The smartphone parade won’t be as lively this year as it has been in past,” said IDC senior research analyst Kevin Restivo in the company’s report. “The mobile phone user transition from feature phones to smartphones will continue in a gradual but unabated fashion.”

Looking forward, the company predicts by 2016 Google’s Android OS will still be the market leader but will have seen a significant portion of its userbase eroded by Microsoft’s Windows Phone — if Nokia can maintain its strength in emerging markets. IDC estimates in five years’ time Windows Phone will be the No. 2 smartphone operating system, passing Apple with a predicted 19.2 percent market share to iOS’ 19 percent.