Hi. To seize the telephone line you need ~200 Ohms across the conductors.
The 600 Ohm transformers are to sort of near match the AUDIO impedance ; NOT the DC load to seize the line.
To inject to or extract audio from the telephone line you should use a
8 Ohm audio output transformer winding in SERIES with ONE of the telco conductors. The primary of any higher impedance can source/inject audio to any other circuits.L1----------------8------- RD 200 L2----------------SW------
RD= ring detector circuit in parallel to line
8 = one transformer winding in series to one line SW= seize/hangup switch or electronically controlled relay 200= resistor, ½WattIf the transformer resistance is in the neighborhood of 200 Ohms and capable of conducting 50 milliamperes, it can be used as both the DC resistive path and the audio coupling.
To hang up you disconnect the DC current path anywhere it be and leave only the ringing detector in circuit.
The ringing is stopped by the telco central office when DC current flows in the loop.
Miguel