I understand that you are having some issues with the SlingPlayer for BlackBerry application since once you install the application on your Mobile device, it asks for the registration process.
This specific scenario will arise if you have already tried to install the SlingPlayer for BlackBerry before using the same Mobile device. This is the only way that you can get this specific message. If you want to avoid this specific situation, you'll need to use a different Mobile device. In all case, I encourage you to check the following article in order to get the information about the supported Mobile devices:
Hope this helps!