The PBX Center application can recognize calls from certain PSTN numbers as "local users" calls. If you call the PBX Center application (usually - the main company PSTN number) from your cell or other PSTN phone, you are asked for your Access PIN. When the PIN is accepted, you are connected to your Service application.
To make the PBX Application recognize your "home calls", your Account should have a homecall-pstnNumber alias, where pstnNumber is your PSTN number (digits only). If your number is longer than 10 digits, use only the last 10 digits of it.