XB7 Question

I just got the XB7 modem and have a question for anyone who might be able to help:

On the back of the modem, there are two (2) phone jack/ports but the one marked "2" has a label that says "Enroll to turn port on".  What does that mean? Does it mean the 2nd phone port won't work unless I enroll in some program? I ask because I have Xfinity's phone service and a fax machine too that needs a phone port.  I actually only plug the fax in when I'm making or expecting a fax but I still would like to know what that means and can't find instructions for that anywhere.

Thank  you in advance!