In regards to TOS and FON: That would be on the owner of the broadband servive. You wouldn't be liable.

In all honesty I have "stolen" WIFI access for Maemomapper when on the road and away from the hotel. However I agree that doing VOIP or other high bandwidth stuff over someone elses line without permission is really rude and I would bet is definitely illegal even if actual access to the wifi point itself isn't covered under the jurisdictions definition of "theft."

For those who claim that leaving a wifi point unlocked and broadcasting is equal to "not theft." I suggest hopping into a running car with unlocked doors and see how far that "freely accessible" argument holds up. Theft is not defined by accessiblity but by permission to access.