Those types of announcements come from CO and network switches, depending on the condition of the PSTN. They usually have a signature on the end that may provide some info indicating where the call stopped or was blocked. Each carrier or provider may have their own type of signature format, for example: AT&T uses 714-95T, or The Telephone Connection uses TTC-SW01.
It does not matter what kind of lines you use on your system.
....JIM....