not always...for example an establishment may have fios, Cable Co telephone service, voip, flex T1 where there is a T1 circuit delivered that carries voice and data and has a powered channel bank, etc, etc.
You are inferring that you would hook up a FACP telco line to a VOIP or T1? That would also violate 110.3(B), the UL listing of the panel and common sense.
All FACP's that take a analog phone line, must be on analog phone lines (POTS).
Ok, assuming we ignore the fact that Fire Alarms are not supposed to be on VOIP, is the demarc equipment regulated by the public utility or NEC?
My point there would be, the NEC, and the prohibition against using a GFCI, would be moot.
Also, Article 760 would not apply to box the supplying the phone service.
I freely admit, using a GFCI on a FIOS or cable modem is a bad idea, and may even be spelled out in their instructions, but its line power, that is normally a plug and cord, is not regulated by the NEC.