For the blackberry, you can go to the mobile store (http://mobile.slingmedia.com/) to download it. As long as your Blackberry is listed as one of the compatible phones (http://www.slingmedia.com/go/slingplayer-mobile).
As for the iPad, the native Slingplayer Mobile for iPad isn't available yet. The Slingplayer Mobile for iPhone only works with the iPad in compatiblity mode. The quality isn't so great since it's try to stretching a 320x240 encoding across the 1024x768 screen.
Yes, since these software are offered by seperate markets, you'll need to have seperate liscense. Each market has their own advantages in liscensing.
I understand why Sling stopped developing for the Blackberry for a while with its aging OS.
Now that BB OS 10 is rolling out, is there consideration of developing a player for the new OS and the larger screens, and faster processors, and faster 4G speeds, that are all available on the new Blackberrys? Surely it's at least as profitable as the Windows Phone.
Anyway looking forward to hearing Sling still cares about this still sizeable market.