Well gunit0072003, if you want to get technical: DSL Modems are called so; because that is what there are. They are modems. There is no digital signal coming from the Central Office. It's modulated frequencies. Just like their older counterparts operating at 56k. What sets the technology apart is the use of how the copper wiring is configured. ISDN in contrast is a true digital signal, meaning voltage levels are recieved and transmitted. Curiously enough, they are not called modems. An ISDN device is a terminal adapter.