An application for only people who own a blackberry phone. It is live messenger on the computer, but for phones. Some people think it is a waste if they have texting. You add people by entering their PIN and wait for their answer. It's slightly like facebook chat, but of course not on facebook. You can also PING people, which can be used to get their attention. Also, when it is first sent, near the side will be a small D. This means it is unread. It turns into an R when it has been read, so you know if you are being ignored or not. It can also be known as BBM.
Blackberry Messenger is just like texting, what's the point?