You're supposed to be able to play the same account on different windows devices by using your facebook login credentials. There are problems with this though, and it's just windows/windows phone. It affects iOS and Android also. There are numerous issues the developer is working on.
And just an FYI on cross-platform support, there is none. It is because Windows/Windows Phone is using Windows servers and databases, iOS and Android is using Linux. The developer made note that even though they *could* make the two platforms talk, they stated they will still be no cross-platform support due to "other" issues. When reading the forums a little deeper, those other issues involve license agreements and/or security.