Verify senders are dialing the correct number and you are providing the sender with the correct fax number for your unit. If you have a second telephone number at your location or a cell phone, you can test the number yourself. Dial your fax number from the second telephone number or cell phone as if you are sending a fax. Then, pick up the external telephone handset and/or press the Hook key on your machine. Determine if what you are hearing on the phone you dialed from is consistent with what you are hearing on the machine. For example, if you hear ringing on the dialing phone, but don't hear dial tone on the machine, then there is a problem with the line or the number you are dialing. In this case, you will need to contact your local telephone company for assistance.