Joe had an older Mac that would allow him to send a fax through OS X, but his new computer won't do that in Mountain Lion. Leo says that was abandoned in the new version of OS X, so he can't do that function anymore with that old fax/modem. Joe needs a voice modem for faxing that's compatible with Mountain Lion. It'll likely need to be external. Leo prefers to use an online fax service, like eFax or MyFax.
If you've noticed your internet connection speed slow down to a crawl often, then there are things you can do to diagnose and fix the problem:
John keeps getting errors when trying to dial up to Net Zero's service. It could easily be that the computer he's using doesn't have a modem. He says that he does have a modem because he has what appears to be a phone plug on the back of the computer. Leo says that can easily be confused with an ethernet port, though. The next place to look is Device Manager in Windows to see if there's a modem listed there. If not, then he most likely doesn't have one. He could buy a modem if he can find a place that still sells them, but Leo doesn't think this is the best way to get on the net anyway.