/me puts on his Intel Home Networking certification hat

Nope, HPNA technology will in no way interfere with any other telephone line usage, including voice, fax, 56k modem, DSL, home security or anything else.

It works similar to DSL, basicially so high above where normal modems use the line they can't hear a thing.
(I wish I had all the tech specs from that Intel class, but that was at a previous job and they didn't let me take home my training books)