you have to contact your phone company to set it up and for pricing.
they'll send through a double or triple ring, or a stutter ring that your HP AIO will 'listen' for and will pick up only when it hears it. this ring would be used when someone calls the second number assigned to your physical phone line.
this second number would be your incoming 'fax number'.
even without that service enabled, you can still fax out as long as you've got it connected to a phone line.
i do recommend not sending or receiving faxes if you're using a voip platform, such as phone delivered via cable or dsl. they compress the traffic as it turns from analog to digital and that can result in unreliable fax message transmission/reception.
I'd test it out on a FIOS based system, as they generally have a lot more bandwidth available than cable/normal dsl and don't have to compress the voice traffic as much, but there's no guarantee whatever FIOS service you may be using doesn't compress the traffic anyways (thus resulting in unreliable fax services).
Last edited by kc8ykd; 01-11-2011 at 21:30..