How long should you wait to call someone again after leaving a message and they have not called back?

Well that all depends on who this person is to you, how important what you have to tell them is for example if its an emergency you would probably keep calling. But if its someone you are interested in and your not sure they are interested in you I wouldn't call back again wait for them to call you. If a few days go by, try one more phone call, if they don't respond they are not worth your time anyways.