I don't think SL on a cellphone is something I would want; it runs find on our laptops and that is as portable as I would want to go.
SL is visual and small screens don't do it justice (at least not on a cellphone). I do have a video iPod tho and the picture there is really great...but it is a download not a stream.
The trouble with SL on a cellphone or small device is the cost for the streaming and the visual quality.
Maybe eventually but not now I think.