Hmm interesting fact about Pandora! I've been using it for over 5 years now and it had the paid option way before the app came out. But wile you are using an app, you have an option to log in into your paid account or listen to it for free.
The tricky thing is, Pandora app is just a portal or a link so to say to their already existing services (which could be accessed thru a webpage).
Satellite radio has the same option, Sirius has an app which allows you to listen to the radio by using your existing account.

If the argument is to be presented, I'd say the one app that should be targeted is AT&T GPS app. They have a subscription built in, even under the description of the app it tells you that you will be charged monthly fee from the point you install their application.