How to identify a DSL Telephone Line

[chasbo@xxxxxxxxx]

With the need to install a filter on a DSL phone line when an alarm
system is connected to that line, is there a method that any of you
use to determine if the line is POTS, a DSL line which is also used
for voice, or when dial tone is supplied by a Cable company?

Asking the customer is an exercise in frustration, as they in most
cases don't know.