Apparently, on P-series, FXS ports don't differentiate internal/external calls.
I saw that Yeatar, in "custom configuration" has published a script entitled: "Script to configure distinctive tone for FXS port".
It's difficult for an integrator who doesn't know Asterix,
why not add a function that would make it easy to add this capability?
(This is sometimes very useful in small configurations, and other manufacturers' IPBXs often do it natively).