Does this happen with all calls, or just some? It sounds like an issue with your service provider. Don't just go off of your phone bill, call in and submit a trouble ticket/service call. They might give you the run around, but firm and remind them that you are the customer, and they need to take care of you. Insist that they send a tech out, and have the tech show you that the caller id is working. Also, if you or a friend have one of those caller ID boxes, plug that into the phone jack and call your number from a cell phone. That will show you if you truly have caller ID.
Usually answered in minutes!