What you are describing is the "free" services, not "freemium" services. Freemium means trialing a product based on usage as opposed to trialing it based on ti

What you are describing is the "free" services, not "freemium" services. Freemium means trialing a product based on usage as opposed to trialing it based on time. Once your usage goes over a threshold you are an active user and you start paying for the service. That's our model on JotForm and it works well for us. One of the best examples of this model is evernote. I remember they were saying something like if the users stays active on their product for n months, they will almost certainly become a premium user.