MAXG,
The phone system we have is a Nortel ICS 4.0. I have a "loop" tape device hooked into Violet/Green and Green/Violet pair on a block. (The other block has the phones hooked to it) I have verified that the connections in fact have a signal on them. This signal is coming from the device's 600 ohm output. There is also an 8 ohm output that does not go to the block, but instead into the floor of the closet with other lines. An oddity I note is that if I disconnect the 8 phm while monitoring the 600 ohm, I loose the signal completely...
Thanks,
SIDFRED