There is a growing trend towards free products or services that are based on advertising revenue. Just think about all the Internet portals, Web 2.0 companies and the like. Some time ago Eric Schmidt (CEO of Google) said that mobile phones should also be free, and instead of charging mobile operators should place targeted advertising.
In my opinion as we move forward more and more services will migrate in that direction. As long as it is possible to survive offering certain services for free while generating revenue through advertising or other methods someone will do it.
More over as technology evolves companies will be able to deliver much more relevant advertising to customers, improving the effectiveness and reducing the annoyance at the same time. What other services could migrate into the “free-advertising” model? Gym, newspapers, wireless internet, haircuts?