Install Blackberry Messanger

1. 1
   Install the latest Blackberry desktop software. It can be found at www.blackberry.com
   This is important, because you might encounter errors with older versions.
   
2. 2
   Connect your blackberry to your computer with the USB cable, and start the desktop manager. You must wait until the title bar stats that your device is connected
   
3. 3
   Go to the application loader, and scroll trough the list you should find blackberry messenger in there some where. Make sure its checked and click next. Follow the directions and your good to go.
   
4. 4
   If your desktop manager says that it cant find any applications for your device, this means that you need a newer version of the blackberry desktop software. I recommend V4.6 It works great for my blackberry pearl.
   
5. 5
   If this fails, then you should do a complete restore of your device, which is also done with the desktop manager. Just be sure to backup all of your data first.
   

Source: http://www.ehow.com/how_4609266_install-blackberry-messenger.html
Read more: How to install Blackberry Messenger | eHow.com http://www.ehow.com/how_4609266_install-blackberry-messenger.html#ixzz1BvNP9y9K