An old thread here but I just thought that I might add a comment...
For analogue equipment, the ring detect circuit that hangs across the line in idle state has a series of resistive and capacative components. Using an ohm meter testing toward the "phone" the power from the meter momentarily charges the capacitance (battery) in the circuit when connected and then discharges. Reverse the polarity of the meter & battery with respect to the line and the the capacitance is charged in the opposite direction and discharges. A linesmans test set would be ideal but an analogue ohmmeter with a line reversal switch wired in would do the trick.
Once you've tested a few phones and faxes etc you'll know what to expect for a phone, or an open, or short circuit line. You can either test the cable pairs, or look back towards the cables from the PABX ports to make your list depending on whether you want to work with pairs, or ports, as your reference.
It will take a little bit of time to set up if you can't get your hands on a test set specifically built for this purpose but once you've done a couple, then you can get through hundreds of tests very qickly.
From memory, a meter with an 80 volt supply, a large analoge meter movement, and a built in reversal switch or button is ideal.
2 microfarods used to be the capacitance value in one phone. Some phone equipment is down to 0.5 uF or even less now I think, but anything under 0.2 uF is probably an open circuit. With the right combination of meter and battery, then an 80% deflection on the meter is a phone, and 10% or less is an open circuit. Flick the reversal switch back and forth to retest. If the needle stays up you have a short circuit, and if it hits the 100% mark with force you have a couple of phones on the same line.
It's very handy to know if there are 2 phones on one line, because you will have to split these services into 2 different services, if the new extension is digital or I.P.
Regards,
Munz.