I have comcast triple play. I wan replace the xfinity rental modem with my own equiptment. The Motorola modem I have does not have a connection for a voice line. Can I use an adaptor which allows me to connect an RJ11 (phone line) to an RJ45 (ethernet cable) & plug into the ethernet port on the modem?
What model of Motorola modem do you have? I would doubt a simple RJ11 to RJ45 adaptor would do what you want. It would have to be some sort of ethernet gateway device that allowed an RJ11 connected phone to talk to an internet service for phone calls.