Panasonic KX-TD500 System Reference Manual page 288

A. Treatment of the call transferred by the VPS
1. Direct Call
1-1.
1-2.
The treatment of the call from the VM extension varies depending on the
conditions.
The following detailed information explains the treatment of a call from
the VM extension by the types of the call.
To an extension
Caller
Transfer
VPS 1
The type of the DTMF tones sent to the VPS depends on the status of the
called extension as follows.
Code Call State
Ringback Tone
A 1
Busy Tone
B 1
DND Tone
B 3
Answer
A 2
To another VM extension
Caller
Transfer
VPS 1
A call from the VPS does not ring another VPS whether it is idle or not.
Code Call State
Reorder Tone
B 2
3-F-28
Ext. 1
Conditions
The Ext.1 is idle.
The Ext.1 is busy.
The Ext.1 is in the DND mode.
The Ext.1 answers the call.
VPS 2
Conditions
The VPS 1 is inadvertently connected
to the VPS 2