No way to know what the call is until you pick up the phone and listen for beeps. Best thing to do is hook the line from the wall to the modem In. Then go from the Modem Out to the Phone/Answering machine. Normally then the answering machine will answer every call but the modem will be eavesdropping on the call. Then if it starts beeping like a fax the modem will just pick it up. That's how it works with normal fax machines anyway.