If by this you mean ,should I replace the digital phones with regular analog phones? I can infer that you already have a PBX if you are using digital phones so no don't replace them. You need to augment the PBX with a voip gateway and configure it into your dial plan. If the PBX and phones are so old that you are going to replace them anyways, you can look at analog phone switch banks or going completely IP. I would do the last if it were me. The cost of decent buisiness VOIP phones have way down from a year ago. As far as replaceing the PBX, there are several "out of the box" solutions based on asterisk that would probably fit your needs and pocketbook. Look around a bit or drop me an e-mail if you would like more information.