I phoned RCN to ask, and they told me very clearly that the cable boxes are not free. Maybe the person I spoke with was wrong, but that's what they told me.

I have a dual tuner Tivo and if I get a box, it becomes a single tuner tivo. So I don't want a box if I don't have to.

Incidentally, I still seem to have the same service I had before; my channels have not gone away. Maybe they haven't gotten to my neighborhood yet?