Note that the phone line from the modem does NOT plug-in to the RJ31X. It would have to be wired into the rear of the jack. CV will do the wiring for you, although they may take a brute-force, run wires back-and-forth approach when there may be better ways.
Better ways like what this guy did, cleverly installing a second RJ31X - »
Re: Optimum Voice installation wiring/jack question