Unfortunately, (since I'm a noob to this bb thing) I deleted the Blackberry Messenger off of my 8830 before I realized that I wanted to have it on the phone...lol...yeah i know...anyway, I tried the OTA download and the "connect your bb to your computer via usb cable" and neither of them said the bb messenger was supported on my device...but it was on the phone when I bought it...
Go to the Verizon website and download the device software bundle and install it on your computer. Then, when you hook up via USB it will update all of your software. In desktop manager go to application loader. You will probably need to put a check mark next to the unchecked Messenger app. Download is here Verizon BB Software