Yes. If the Comcast box has a typical female RJ-11 modular telephone jack, and your home's telephone wiring is connected to the box with a telephone cord, all you need to do is to unplug the cord from the Comcast box and plug it into the telephone jack on the OBi box. Of course, you also need to connect the OBi to your home's network via an Ethernet cable or optional WiFi dongle (Ethernet is best). So, you could just place the OBi right next to the Comcast box and plug things in.