WhatsApp is a very popular cross-platform messenger for mobile that works via data plan and is available on most platforms like iOS, Android, BlackBerry OS and Symbian. Unfortunately, Windows Phone is not on the list but it might be soon!
WhatsApp is looking for a person with strong C/C++ programming and debugging skills as well as strong Java or C# programming and debugging skills. Windows Phone 7 is based on C# so the job posting could be an early indication that the popular app will soon join Redmond-powered phones.
One of the many reasons why Windows Phone is not popular at the moment (lack of features currently at least until Mango is out) is that there are a couple of key applications, like WhatsApp for instance, that aren't available for the platform. Skype will hit Windows Phone once Mango lands and our guess is that other key applications will start arriving to the platform once the fall refresh makes Windows Phone gain some more market share.