The server's addressing would need to be the same as the ones stored in BBM software on BlackBerry phones + all the other places where it's needed to make BBM work. That's just the addressing, who knows what else is designed into making BBM work across a group of accounts over a network. If you create a new app with its own details, theoretically you can, but it wouldn't be BBM any more of course. Why would you consider this when you can download any number of apps where someone has already done all the hard work for you?