In the fight to unwire cities, Google might be one of the bigger names in the business, especially when it comes to the potential for location-based advertising. But Mountain View-based startup MetroFi, which champions the free ad-supported WiFi model, just announced a high profile ad-pushing partner of its own: Microsoft.

MetroFi and Microsoft say they have partnered to bring “locally relevant MSN content and services” to the city-wide network in Portland and plan to incorporate Microsoft’s adCenter technology into the service as well. Microsoft referred to the deal as a “pilot.” Perhaps like Google, Microsoft could be using a city WiFi deployment as a test bed for different types of advertising, including location-based ads.

MetroFi’s CEO Chuck Haas says MetroFi’s ad platform can help advertisers target neighborhoods and zip codes by using location information from the access point where the user is connected. At launch Microsoft’s general manager in the MSN Media Network Group, Sam Klepper, says his company will offer local information such as weather, news, restaurants, nightlife, movies, Portland government services and local search. Though, at the time of launch Klepper says Microsoft will not be serving locally relevant advertising.

Signing up Microsoft is a substantial win for the small startup that has raised $15 million to date — which isn’t that much considering it’s building and running large networks. It’s also a good sign for the ad-supported WiFi model, which has been viewed with considerable skepticism.

The major issue I’m confused about is the business agreement between the companies and if Microsoft is putting up any money for the network. I asked both companies on both these questions and they both refused comment. Why be secretive?