I'd like to attach a POTS to the MIC/EAR ports of a voice modem.

I understand they call it a 2-wire/4-wire interface, but I never saw one.

Any hint ?

I guess I need some current to circulate for the POTS to work.

AFAIK 20mA is what is required. Being 600 ohm the standard resistance of a
POTS, 12 V DC will be enough, on paper. Right ?

I hear that the DC voltage supplied to POTS must be very clean.

How should I filter the 12V DC supplied my a cheap external power supply ?

Thank you

Duilio Foschi