An inbound marketing / pricing strategy to attract customers is to make part of a real product free; with upgrades to priced products, services.
  • Features
  • Functionality
  • Virtual goods
Test for a limited feature set or select number of users, but preferably not for a limited amount of time. 

A good mantra is not to try to make money on people using your product as a toy, but rather on those who use your product as a tool. 

Freemium requires you to have more or less zero duplication and distribution costs which makes it impossible for certain businesses.

Also See