Next Maemo is not totally open source, but nothing's bulletproof, and I don't think they'll even be specifically trying to stop us from adding that until it happens.

That said, Raiden's right, it's unlikely to happen without substantial help from Nokia; OTOH, the Fremantle releases seem to have some measure of phone support included -- whether that means the "N900" (RX-51) will be a phone, will be a few tweaks away from being a phone, or will have no phone support at all, we can't say at this point. What it does mean the platform is intended to support phone-capable models at some point. The likelihood of phone calls on the RX-51 varies strongly with the applicability (and quality, quantity, etc.) of any phone support from Nokia.