Robert Williams, Microsoft's former Senior Director of Windows Phone business development, has joined Amazon this month. Williams' lists his new role as Amazon's App Store director in his LinkedIn profile and a tweet, spotted by Win Gadget News, reveals he's still using a Windows Phone to check in at his new employers headquarters in Seattle.

Previously responsible for Windows Vista Ultimate Edition, Williams is the second high profile exit from Microsoft's Windows Phone team to Amazon in recent months. Earlier this year, Brandon Watson — the former head of Windows Phone Developer Experience at Microsoft — quit the software giant to join Amazon as Director of Kindle Cross Platform team.

Rumors of an Amazon smartphone have started to heat up recently after two reports suggested that the company is testing a device that may go into production later this year. If Amazon is indeed developing a smartphone, then it's reasonable to assume the company would lean on employees with smartphone experience or recruit those who have played an important role building a smartphone product at a rival firm. There's no evidence that Watson or Williams are working on an Amazon smartphone, but if the rumors are true then we'll likely see a four- or five-inch device later this year.