Sorry, but you can't switch between those 2 platforms. You'll need to purchase another license. that's simply Sling Media's policy to this point.
You can switch to a new device on the same platform, but a license is required for each patform being used.
Most of us hated it even more when we paid for an iPhone version and had to purchase an iPad version as well for just that reason.
and they are on the same platform? geez...
i gave up blackberry and now run IPHONE, IPAD and a android phone (backup), and trecently trying a windows 7 phone. so i would have to buy a license for each one to be able to use my many slingboxes around the house....
right now none of them are working...got to figure that probably out also.