In a freemium model there don't have to be any ads at all! Your basic service can be totally free, provided you can justify it as marketing expenditure with th

In a freemium model there don't have to be any ads at all! Your basic service can be totally free, provided you can justify it as marketing expenditure with the conversion rate to paid services. The biggest problem I can see with running ads on the free tier of on a two tier service is that the people most interested in buying advertising will be your direct competitors. It might not be too smart to give them easy access to your user base.