I honnestly disagree on the fact that there isn't place for more players in the mobile market. It's a constantly expanding market and fact is, a BlackBerry CAN "interact" an android device. If you have a Windows Phone, you can call IPhones etc., you are not "excluded" from the others. You can't compare the mobile device market to, for example, an operating system market where a Windows computer can't really "interact" with an Apple computer.
Of course, when big players like M$, Apple and Google enters your market, you are going to lose market share no matter what you do. At the end of day, RIM has a decent amount of fans out there and they will be able to exist. Their devices are unique and provide something different for their users.