The tel-14 back plate has 4 connectors, each line uses one RJ45 and one DB-9 connector. The DB-9 connector connects to the telephone line via the DB-9 to RJ11 adapter (CC part # 770025), the RJ45 gives a 4w connection and call signaling when used with a matrix system. You can use the RJ45 for a 4w audio signal to/from other audio equipment. The pin out of the RJ45 connector is as follows: 1- call send +2- call send –3- audio send+4-audio receive+5- audio receive –6- audio send –7- call receive +8- call receive -