A lawsuit was filed earlier this year in California on behalf/by wireless subscribers who received higher than expected charges for ring tones. Jamster has been accused of not providing transparency in their pricing policies. See these articles: Article 1, Article 2, and Article 3.
These stories didn't resonate much with me until I received written (= on paper delivered by USPS) notice from Verizon this week that I would be charged $0.99/month for my ringback service.
I'm not sure yet if this is voluntary on Verizon's part or mandated by the state of California. (I do plan to find out) In any case, I think it's a great strategy because it was not clear in my mind that I would be paying monthly charges for the service. Only piece missing was a clear opt out strategy.