If you receive a voice call and the machine is in Fax/Tel mode, it will start to sound the F/T Ring (a fast double-ring) after the initial ring delay. If you pick up the call on an extension telephone you can turn the F/T Ring off by pressing # 5 1 (make sure you press this between the rings).
If the machine answers a voice call and fast double-rings for you to take over, you can take the call at the machine's handset by pressing Speaker Phone.