John Chen stated that BBM for Windows Phone was coming in July and it looks like he will hit that target. CNET spotted the beta of BBM for Windows Phone showing up in the Microsoft Windows Store on Monday. It is currently in beta and they are only opening it to those who have received invites sort of like how they did with Android. The app is compatible with Windows Phone 8 and 8.1 but BlackBerry confirmed that it is currently just a closed beta stating that:
"We have been using the Windows Phone storefront to help conduct a closed internal beta to test the BBM for Windows Phone app. We plan to use the Windows Phone store to facilitate a broader external beta in the coming weeks. Only users who have been whitelisted to participate in the beta will be able to install the app. More information on how to participate in that external beta will be available through the BBM blog shortly."
I am sure it will help once they expand to more platforms. I just want to get a desktop or web client and the ability to run it on multiple devices… Best of all would be read/unread status in groups.