Microsoft and Nokia will hold a press conference on September 5 where the companies are expected to make an announcement about Windows Phone 8, the next version of Microsoft's OS for mobile devices.
Nokia is a close Microsoft partner in the mobile phone market, where both companies are striving to improve their standing.
In the first quarter of 2012, Nokia's global share of mobile device units sold fell to 19.8% from 25.1% in last year's first quarter, according to Gartner.
Meanwhile, Samsung knocked Nokia out of first place when it grew its market share to 20.7% from 16.1%. Apple also improved its position by increasing its share to 7.9% from 3.9%, Gartner said.
In the smartphone segment of the market, which is where the growth is happening, Apple and Samsung ranked at the top with a combined share of units sold of almost 50%, while Nokia's share was 9.2%, according to Gartner.
Viewed from the angle of smartphone OSes, Android ranked first with 56.1% of units sold, followed by Apple's iOS with almost 23%. Microsoft came in a distant sixth with a 1.9% share, according to Gartner.
Nokia's Lumia smartphone, which runs Windows Phone OS 7.5, got generally good reviews from technology journalists but its sales have been disappointing.
Windows Phone 8 is a significant upgrade of the OS that will be closely aligned from a technology standpoint with the upcoming Windows 8 OS for desktop PCs, laptops and tablets, which is slated to ship at the end of October.