We don't have a good path for native apps, yet. There have been a few experiments using Persona in native iOS (Pancake) and Android (Soup) environments, and it apparently works great in PhoneGap apps, if you use the ChildBrowser plugin.

The bug to watch is this one: https://github.com/mozilla/browserid/issues/2034 supporting environments without popups will clear the way for good native SDKs.