Almost all ads to some degree are something that "no sane person would ever want". The difference is that Sellaring makes ads that are not easily ignored. In contrast, the on-screen ads on Android's AngryBirds are easily ignored even if animated and although I don't run AdBlock I rarely consciously see ads on webpages. The human brain is an amazing filter.

I'd say the advantage to Sellaring is that 1) the person actively listens to the message (it's more difficult to filter out audio ads as they're listening for the call to start) and 2) it's using up "dead time" if the ring was going to go for longer than 10 seconds anyway.

I can see both points of view but if you're not paying for the app... It also provides a strong incentive to upsell to the paid version of the application that loses the advertising as well.