Now, you can see Google's patent filling on advertisting funded WIFI. MsGraph of Threadwatch says that the filing is "Short and easy to read. Lists different ways for how they might display advertisements to offer free or reduced-rate wifi access." According to him Google is left with two options, either create their own network or build partnerships with other providers.
Here’s a fraction from the patent filing:
 In stage 610, the first entity, in turn, credits the WAP provider with a portion of the advertisement revenue. The portion of the revenue may include a flat rate, a percentage of the advertisement revenue, or a combination thereof. In one embodiment, the first entity identifies the WAP to be credited via the IP address.
 As a result of receiving a portion of the advertisement revenue, the WAP provider is may cover the expenses of providing the WAP and may recoup a profit, while providing end-users with access to the WAP at a reduced rate.
 In alternative embodiments, data other than advertisements could be inserted by the first entity into the view presented to the end-user accessing a WAP. For example, the data could in the form of a message, or a static advertisement that does not include a hyperlink.
 Furthermore, the processes and architecture described above may be used to provide wireless access at a reduced rate for multiple WAPs, including multiple disparate WAPs.
If you want to find out more on the system and method to provide advertisements, Click here.