charging for premium features, as Spotify and Skype do. Advertising generates revenue from in-app or online ads—a business model employed, for example, by YouTube, Facebook, and many news websites. Bait and hook provides a free or discounted product and generates revenue from selling another product or service that locks in the customer. Take, for instance, iTunes: while the product itself is free, it is only truly useful when combined with a comparatively expensive iPod, iPhone, or iPad. Once you have started using Apple products, you are locked into the Apple ecosystem.
