FAX-878 FAQs & Troubleshooting FAX-878 Not your product? Sort by: Updated Date Popularity 1 Results 1. 11/19/2012 I have an external telephone answering device on the same line as my FAX and have the answer mode on my FAX set for TAD mode. How do I know if an incoming call is a telephone (voice) call or a fax? Telephone FAQs & Troubleshooting