Ask HN: How do read it later sites make money?

[bobcattr]

This came up in another post and I wanted to know how sites like pocket, read it later, readability and others make money? Instapaper is the only service with a semiclear business model, they sell subscriptions and apps. The others don't sell apps, their apps are free. They don't sell a service their service is free. This leads me to believe they are selling the users.

[amccloud]

I also was wondering this exact thing recently. Hopeful someone can provide some insight!