Can't use bridge mode with dynamic IPs?

yes, i believe so. if you need dynamic IPs, i think you need to purchase your own modem. i remember that i had an SMC8014 that a CSR told me he could not put it in bridge mode.

that said, i have heard that some people have had success over at the DSLreports.com forum. specifically, the "Comcast Direct" one. or potentially IM Comcast_Jon here.

truth be told, if you have a dynamic IP, it might be a better value for you if you do purchase your own modem; at least, it will save you the modem rental fee.