Now when Google launched Gtalk for Blackberry it was avaliable across the board no matter what type of BB you had. Yahoo! on the other hand give the royal FU to anyone not on Rogers, Sprint/Nextel in the US.
You can download Yahoo! Messenger if you are on one of the above mentioned US carriers and a few carriers overseas. Otherwise you aren’t going to be getting your Yahoo! fix anytime soon. Yahoo does have a deal with only T-Mobile for Yahoo mail on your blackberry, but I don’t know a single person besides my mother with Yahoo! mail.
Oh well, T-Mobile does include a messenger that works with Yahoo!, but it has a text message fee with each message.