Sharing broadband with other people for VoIP.... FON vs Free

I've just got back from the VON conference in Berlin - I'll be posting over the next few days about VoIP, SIP and other good stuff.

One thing did stick in my mind though - you know all the fuss about FON breaking some ISPs' terms of service because you're sharing your broadband access, by letting other wireless users do VoIP via your access point?

Well, apparently French operator Free (owned by Iliad) is going to be doing the same thing itself, with its own customers' APs and broadband. As a Free customer with a dual-mode handset, you should be able to use the WiFi capabilities of all the other Free customers' home gateways - potentially over a million hotspots in residential areas. The gateways have both public and private SSIDs.

The question is, if someone else is using my broadband, officially sanctioned by the ISP, how much are they paying me? And what happens if I live above a popular cafe or next door to a university - how many concurrent users can sit on my network, and does the Free box prioritise their realtime voice traffic over my email or web browsing?