-- Thank you for clarifying the version of the two filters that went U/S.
As for your second point, the answer is none. Consider what happens when a call is initiated to any line. A (time modulated) AC voltage is applied across the pair. Acceptance of that occurrence was built into the initial ADSL standard . . . which continues into the current VDSL2 standard.
I have not done so but that could be an interesting experiment. Ideally one would use a dual "beam", storage O'Silly Scope
Connect channel one to the xDSL output from the SSFP and connect channel two to the telephony output. Call the relevant telephone number for the line from a mobile phone and adjust the trigger level, channel gains, etc. What is seen?
Could somebody perform that experiment, please? Perhaps Eric
? (I only mention those two names because I have a very strong suspicion that they both own an O'Scope.)