I got a new Blackberry Curve yesterday, and the first new application I added to it was chess.com mobile. The installation was very easy, it just texted a link which then downloaded and installed the program. Setup was not so easy though. I don't know if it's user error or a program limitation, but it refused to work with a password that included numbers. The data entry method for the userid and password was a little bit weird too, but that's understandable given that the bulk of the programming work needs to be the chess board interface.
The chess interface wasn't bad at all, IMO. Trackball to the piece to move, click, trackball to the square to drop, click. It took 2 confirmations that the move should be submitted, which is only mildly annoying. I'd prefer that to the chance that it would misclick like other mobile apps are prone to doing.
It wouldn't be an interface I'd want to use a lot, but it's a nice way to check if any games are short of time and get the moves entered.