The BlackBerry Messenger app for Windows Phone might be a beta, but it's still a worthy complement to the Android and iOS versions. With it, you'll be free to chat with BBM users across platforms, sharing photos, chatting with groups, and more.
You're limited to chatting with BBM friends, but the app behaves just like any other messaging app otherwise. This will make it hard to compete with entrenched players like WhatsApp, Google Hangouts, or Apple's Messages app.
All of your active conversations sit on the chats pane, where you'll see messages from individuals and groups. When you're chatting with friends, you can attach images, audio clips, and contact information to messages.
Anyone you want to chat with will need a BlackBerry account and PIN number. If they already have a PIN, you can just enter it in via the app's contacts pane to get started. BBM will also create a QR code with your PIN details, which should make sharing your info that much easier.
The feeds pane keeps you updated on what your contacts and groups are up to -- you'll find status updates, and any changes to their profile pictures here. The Android and iOS versions of BBM also offer Channels, which are a public groups centered around topics of interest, but that feature hasn't made it to this version of the Beta.