How do you block incoming calls on T-Mobile BlackBerry?

The best way to block incoming calls on your Blackberry (doesn't matter what Blackberry you are using) is to use an app that BerryWAV had developed. It's called Efficient Call Blocker. It works by allowing you to explicitly add numbers to a list where you can block. Using this along with a service like YouMail, you can have the person calling hear a message like "this number has been disconnected or no longer in service."