Microsoft's after a software engineer to help its Interactive Entertainment Business division bring "Xbox Live entertainment experiences to various mobile platforms". Justification for the plural form of platform is provided further into the job posting, where it not only mentions Windows Phone, but iOS and Android too.
A glance at the desired qualifications suggests Microsoft is keen to get Xbox Live titles onto more portable hardware. Applicants would do well to have "experience of Windows Phone, iOS or Android development" and "proficiency in C/C++, C#, Java or Objective C". All those languages cover the mobile platforms mentioned, with C# handling the XNA side of the equation, and one does not seriously learn Objective C these days unless they're keen on iPhone development.
The phrase "Xbox Live mobile experiences" is used extensively throughout the description, which one would hope is HR-speak for "games". Of course, it's entirely possible we're looking too closely into this, and all Microsoft wants is another developer to shore up its recently-released Xbox Live mobile app.