If you are working with campaigns you can set the conditions for your call conversions by opening the Campaigns tab yourself, by adding new Pricing Models.
Next, click on the preferred Campaign name.
Scroll down to the Pricing model part and add a New Pricing Model.
Don't forget to Save your segment to confirm the changes!
In the example below the custom made Pricing Model specifies that all calls longer than 4 minutes, received any time on any day of the week are counted as converted and their value is 10 EUR in commissions.