Why the phone screen displays “unknown” instead of Caller ID once the caller calls through the analog trunk?
It might derive from:

  1. The trunk doesn’t have Caller ID service.
    To be able to confirm it, please connect the PSTN line right to the analog phone and call it via cellular phone to check if there is Call ID on the phone. If there is no Caller ID, please contact the service provider.
  2. Wrong settings of “Caller ID Start” and “Caller ID Signaling” if the trunk has Caller ID service.
    In cases like this, please change their settings. (Select “Trunk”-> ”Analog trunk”, and select the right type for “Call ID Start “and “Caller ID Signaling” in the editing page)