If I'm understanding you correctly the two rooms share a wall? And you're essentially wanting to put a box in the second room that is "behind" or opposite the box in the first room? If that's the case then get a keyhole saw and an electrical box made for remodling. Drill a small hole in the plaster to start the saw and cut out for the box. Mount the box, fish the wire(s) and finish it off with a proper face place to plug your telephone/network wires in.
