I'm a little confused by this non-sequitur. Why would your old Touch-Tone phone care about the details of your back-end connection to the PSTN (copper to the CO vs. VOIP)? How could it tell?
I got VOIP fromTime-Warner Cable more than four years ago and did not have to change any of the phone instruments in the house. That includes the early-1980s Bell Touch-Tone desk phone that we have in the basement. Going to VOIP didn't change my internal wiring at all; it only required connecting that internal loop to the cable modem.
Bob Goudreau Cary, NC