The recent update to BBM added some new features to the application. Right now, BBM users can send messages to other BBM subscribers, make free phone calls to other members anywhere on the globe, and engage in discussions on BlackBerry Channels. You can even share pictures, files and voice notes to other members. Eventually, BlackBerry Video will allow you to have video chats with other BBM users.
One of the cool new features available for BBM users is Glympse. This allows you to set a period of time during which your location can be discovered by selected members. Once the time period that you've selected is up, you are invisible once again
BBM is available for iOS, Android, and of course, BlackBerry. For now, Windows Phone is the odd OS out.
source: BBM, BlackBerry via BerryReview