All you have to do is log into your account and go to Settings ⇒ Public Profile ⇒ Settings & Privacy.
You will find an option called: "Displaying my Services ID" and you will be asked to add the minimum amount a member must have in his account to be considered premium ($1.00, $5.00, etc.). Do not forget to save the changes.
Important!
The Skype ID is required for the members to be able to contact you on Skype and have calls with you!
VIP Members are the exception and will be able to see your Skype ID regardless of your settings.