Kevin Restivo, senior research analyst with IDC's Worldwide Quarterly Mobile Phone Tracker, says that the Windows Phone performance is a validation for direction taken by Microsoft and Nokia:
"Windows Phone claiming the third spot is a first and helps validate the direction taken by Microsoft and key partner Nokia. Given the relatively low volume generated, the Windows Phone camp will need to show further gains to solidify its status as an alterative to Android or iOS."
IDC also say that the growth of Windows Phone indicates there is end-user demand and OEM support:
Windows Phone posted the largest year-over-year gain among the leading operating systems, more than doubling its size from a year ago. Nokia was largely responsible for driving these volumes higher, accounting for 79.0% of all Windows Phone shipments during the quarter. Since Nokia began shipping Windows Phone devices, the company has shipped a total of 20.3 million units and grown the footprint worldwide to include address multiple market segments. Meanwhile, other vendors continue to offer Windows Phone devices, but mainly as an alternative to their signature Android devices. Still, the gains made by Windows Phone demonstrate both end-user demand and OEM support.
It's worth remembering that Windows Phone growth was based off a relatively small base, making it easier to achieve high year-on-year growth percentages. Nonetheless, Windows Phone shipment figures do appear to now have some momentum, something that should continue if Nokia is able to meet the projections it made in its Q1 2013 results.