Kevin Werbach discusses his expectations for municipal Wi-Fi: He envisions cities contributing their physical infrastructure such as light poles as well as funding to support coverage in areas where the private companies might not get a return on their investments. Private companies would do the rest. It sounds like Werbach is suggesting that the municipal network wouldn't be free but would be cheaper than alternative access methods. The networks would also be used by city workers to do their jobs.
There are a couple problems about this discussion over municipal Wi-Fi that aren't usually addressed. One is that while it's a great idea for cities to sponsor coverage in low-income areas, the people who live there will need computers to get on the Internet. If those residents currently go to the library or the public school to use a computer, it doesn't make much sense to cover the whole neighborhood with Wi-Fi. San Francisco's mayor said that no resident should be without a computer, but his wording doesn't necessarily suggest that he's going to try to ensure that every resident has one.
Also, I suspect that if these municipal networks really happen in a significant way, the cellular operators will start raising a stink. Werbach describes competition between the high-cost and reliable 3G networks and the cheaper and less reliable municipal-sponsored Wi-Fi networks. Given the price that the cellular operators have spent to build their networks and to license spectrum from the government, I should think they'd raise hell over a city-sponsored competitor.