Yes, but from my brief searching, it does not seem likely that I will be able to mark mobile Facebook buddies. Facebook simply does not give Adium or any chat client that information.

I do not know if Skype sends any information about mobile devices in its connection metadata. If you use SkypePlugin, I would ask the developer about adding this. I know for a fact that people marked as mobile on Facebook are marked as offline in Jabber, so there is no way to differentiate between offline friends and mobile friends. I will look into this, but it currently does not seem promising.