Re: Virgin Media and old phones
Sky's analogue line spec (BT's SIN should be similar, but I can't find it as quickly)
The interface will recognize a loop resistance of greater than 10 k Ω between the ‘A’ and ‘B’ wires as an off-line (on-hook) condition. A current of less than 3.5mA will not be recognized as a seize condition
The interface will recognize a loop resistance of less than 1 k Ω between the ‘A’ and ‘B’ wires as a seize condition. A current of 10mA will be recognized as a seize condition.
So if you can put a DC ammeter in series with your payphone and measure the line current on- and off-hook.
If it's within the above limits I would suggest to Virgin that their box is not providing an analogue line within specification, unless they publish their own interface specification which is different.
I would also wonder whether your 2-wire Virgin hub connection is correctly converting to a 4-wire BT connection, in particular the earth on payphones was used for signalling to the exchange (for emergency calls in manual areas without inserting the fourpence first) and this might be causing a partial short across the line.
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