Zoom X5v Technical Reference page 54

Note: You should add an answering machine to the X5v or V3 if
you want to install your device at the demarcation point—
otherwise, regular PSTN calls will not get through when
you are on a VoIP call. The answering machine must be
installed in front of the X5v or V3—that is, it must be
connected to the Telco (or DSL) line before it connects to
the X5v or V3. Callers will hear the phone ringing, but it
will not ring at your end.
If you hook up an answering machine to the X5v or V3,
PSTN callers can leave a message if they attempt to call
while you are engaged in a VoIP call.
2995-A 27384 ©2005