@Wewilldoyou if you're prepared to do some VERY SIMPLE wiring you can easily reconnect your old cabled phones, though it does depend what type of master socket you have. If it's not the latest "clip on" Master Socket 5C just say what it actually is.
Assuming a modern NTE5C, your extension wiring will go back to the "5 3 2" terminal block on the backplate, though really only 5 and 2 are needed unless your phones are literally antiques. You basically need to isolate this from the incoming line and run a cable from it to the filter at the router.
When you pop the faceplate off you'll see a protruding plug with electrical contact strips top and bottom. Just cover the bottom strips with thin tape to insulate them. Then get a lead of suitable length with a BT phone plug on one end (for the filter socket) and expose the wires at the other end, you only need numbers 2 and 5, so check with a multimeter if there are more than 2 wires in the cable. A typical BT plug has 6 contacts, though 1 and 6 are often empty, so 2 and 5 are either side of the central (3 4) pair. Any way round is fine.
Pop open the connector on the backplate and feed the two wires in along with the existing extension wiring, no need to remove insulation on the individual wires, just the outer sheath. The sockets are oval to accommodate 2 wires and you slide them all the way in then snap it shut. Refit the faceplate, which might be a bit tighter now with the tape there.
If your phones are VERY old they may not ring with only 2 wires connected. The solution to that is to fit a broadband filter where they plug into their local sockets.
