Do you need to turn off answering machine to receive fax vie fax modem?

No, but if you pick up the phone while a fax is being sent or received, you will hear some unpleasant sounds & the fax being transmitted may be corrupted.

AnswerThis is one disadvantage of using the traditional fax machine, but with internet fax service, there's no need for a telephone line in order for you to send and receive faxes. Since fax documents are transmitted via the internet your can access your fax anytime and anywhere you are without getting a busy signal. All your faxes will be instantly delivered to your online account in formats either PDF,TIFF or palin text.