BlackBerry has made Windows Phone users of BBM feel right at home by using the Windows Phone UI. Keep in mind that not all of the features available to iOS and Android users of BBM will be supported by the Windows Phone version right off the bat. Features like BlackBerry Stickers, BBM Voice and BBM Channels will be added to the Windows Phone version of the app in the coming months.
While Matthew Talbot, BlackBerry's Senior Vice President for Emerging Solutions, gives a number of consumer friendly reasons why BlackBerry allowed BBM to become a cross platform solution, the real answer might have a lot to do with Facebook's huge offer for WhatsApp. The latter was valued by the social networking site at $42 a user. It doesn't take a brain surgeon to understand the additional value that would be placed on BBM if millions of iOS, Android and Windows Phone users were to sign up with BBM. This gives CEO John Chen the ability to consider selling or spinning off the messaging app if things get rough.
source: BlackBerry via WPCentral