Fred Wilson has a very interesting post wondering about whether WiFi should be Public Infrastructure. He also links to a very good post comparing the question to the development of the Boston waterworks system in the early 1800's, where public water spots co-existed with an entity that delivered them for a fee.
It's hard to use historical analogies because they often break down in the details, as we live in different times and there are different forces at work. A few years ago I often thought of the browser wars as having similarities to the railroad and subway building explosion in the 1800's with companies laying incompatible track. Since the 1800's were an era of great industrial growth and the Internet era is a bit over 10 years old (Yahoo celebrates it's 10th anniversary this year) there are broad parallels, compressed though they are. Maybe Moore's law at work.
I'm wondering if free WiFi would really work as Public Infrastructure from a political perspective? Given the times we are living in I could imagine municipalities behaving more like China and censoring what sites people could access. And I also wonder if it is worth the ease of use to take part in a system in which our usage and actions can be easily tracked and recorded.
I might be more comfortable with some kind of super-secure (if there is such a thing) web based service that works like a key so I can access the different services more easily without having to register and set up each time. More like a WiFi calling card. Overall I do think they should be free and sponsored sounds like a way to go. I for one would site through a video-ad if I could get on with my work from a park bench on a nice day.