Internal voicemail only?

Hi there, I am the IT dept for an insurance company. I am currently working to deploy freepbx solutions at each of our 4 offices. So far everything is working great. however my question is, is there a way to setup the voicemail so that only other extensions can leave messages. We do not want customers to be able to leave messages for agents due to legal reasons and etc but it would be really helpful if the receptionist and agents could leave messages for each other. Any help with this would be greatly appreciated. Thanks