It should be possible to push advertising into web and maybe email? As a means of offsetting cost.

As a user I wouldn't mind seeing ads in exchange for free hotspots.

Using frames (ala Google Images, About.com, etc) would make it possible to run banners or similar without damaging individual page markup. With a transparent proxy it ought to be possible to enforce all pages be loaded in a parent frame.

To get more advanced, using AJAX or similar technology to force banner reloads - the proxy could log banner loads and disable access if a banner request isn't made every minute or something, that would bypass basic ad-stoppers (they could still be avoided if you were keen).

If you were to create an ad-free paid service the question would then be how to work it... Usage? Subscription? Combination? I tend to think a subscription with maybe additional usage is best - say $5/mth with a cap of 500MB month - then maybe data charges after that point. That balances out in that many users will not actually make use of the service all the time. People like me are (I think) far more likely to pay a few bucks a month for a service which we may only use sometimes, than we are to pay $10 for an hour of access at a Telecom Hotspot.

If usage costs are created - make it by data, not time because time-based is stupid!