Yes, you can enable fax lines the same way you would your normal phone line. Here is how to set them up:
First, click on the 'Get Started' button at www.nomorobo.com.
Then, choose "Landline" in the first pulldown and then choose your carrier in the second pulldown.
After that, click "Save this Phone Number".
If you have other carriers, click "Add" and choose them from the pulldowns.
To set up protection for each phone number click "view instructions" and follow the steps for your particular carrier.