Bbm is a closed platform but I read that bb is supposed to be soon Providing apps on other platforms and even a pc client. Knowing bb, it will be pricey. This might be completely baseless rumor so TIFWIW
I personally do not miss bbm since all my bb friends also use gtalk, a much more open platform.
i read this rumor on engadget but i cant see how this will happen. why would rim give their best app to other platforms. i have heard many people say bbm is the only reason they use a blackberry and if it makes its way to ios and android they will dump their blackberry. only way this makes sense is if they are planning is to be a pricey paid app though it will still undoubtably hurt their phone sales.