Both Android and Blackberry versions of the Mobile Security Key are coming very, very soon. Real soon! (I'd give you an ETA, but there are too many moving parts.)
In addition, physical security keys for Europe will also be along very soon. We had a few shipping / supply issues, but they're inbound.
I may be blind, but is there a way to remove a Security Key from an account? I linked an iOS from an iPod, but that was a temporary measure until the android app came out.