What is the resistance of a land line telephone
I have used audio transformer P/N 42TM016-RC (from mouser) with 470 ohm resistor in series on the side connected to the phone line to get off hook voltage of approximately 6V. The resistance of the transformer's primary side is 65 ohms. This would give equivalent resistance of about 545 ohms. You can play with the resistor value little bit to adjust the off hook voltage. This combination worked great for audio and sending/receiving DTMF signals.