Dell 2335DN - Manual (Page 188)

If you want to use your computer modem for faxing or for a dial-up internet connection, connect the
computer modem directly to the back of your printer with the TAD as shown here in Figure 2.
Set your printer to Ans/Fax mode and set the Ring To Answer to a digit greater than the rings to
answer setting for the TAD.
Turn off the computer modem's fax-receive feature.
Do not use the computer modem if your printer is sending or receiving a fax.
To fax via the computer modem, follow the instructions provided with your computer modem and fax
application.
You can capture images using your printer and Dell ScanDirect and send them using your fax
application with the computer modem.
Sending a fax from a Computer
You can send a fax from your Computer without going to the printer. To send a fax from your Computer,
install the PC-Fax software and customize the software's settings.
Installing PC-Fax Software