After a series of hints pointing towards a Windows Phone client of the popular WhatsApp program (a tweet about mangos, a job posting and more recently, a teaser image), there’s irrefutable proof that the application is coming to Windows Phone, that is really soon!
If you follow the source link below you will land on the Marketplace page for WhatsApp for Windows Phone. Trying to install the application will return an error though, saying you don’t have permission to download the application (and we’ve tried on a Mango phone). Maybe they’re just waiting for Redmond to officially launch Windows Phone Mango so that the application will go live on the OS refresh. Those staying away from Windows Phone because of it missing key apps, such as WhatsApp, have one less reason to do so.