The Virgin service is for mobile customers who want to increase their monthly calling allotment, and it will appeal to a minority of the mobile-addicted folks. But as I've said before, ad-supported calls will debut in a big way on VoIP services such as Skype.

The price of calls via PC or mobile have fallen to the point where ad-supported services are feasible. Skype should be able to integrate graphical or video ads as a pre-roll before you make your call, and eBay already has the advertising network in place to make it happen.

Source: Marketing Shift