Stuart Lodge commented
I have some WP8 and Droid code working now - https://github.com/slodge/BallControl - working on MonoTouch support - but sadly v1 of WinRT seems not supported for SPP and LE type devices :/
This is a key feature that should be available and exposed via a common API. While the implementations of the BT stack on each platform may differ greatly it should be possible to expose a very generic API for this including discovery, pairing and at least basic communication. From a development perspective I would assume exposing a raw byte level comms as a start (rather than OBEX etc) is sufficient
Michael Mudge commented
32feet.NET has a solution but it requires a custom Mono build. Surely we can do better than that, even if we ARE sticking to the MSoft standards.