Phone switching device

Can someone help me solve a problem? I have
cable hookup for my internet use, so I don't need
a device that switches incoming calls that go through my computer. What I do need is a device
that will recognize an incoming fax call verses
an incoming toll free call. I have a dedicated
phone line that hooks directly to my fax machine. My problem is my toll free number is piggybacked
on top of this same phone number and incoming calls are lost, depending on the call.
I hope I have explained this correctly.
Can somebody please help me solve this problem?
Thanks for your time,
Bill Rhodes