Billion BiPAC 7404V(G)OX User Manual page 124

To take your phone OFFHOOK, lift the receiver then press Hook/Flash until you hear your normal
PSTN dialtone, not your VoIP dialtone. Wait several seconds and then press Check Level.
You should check the OFFHOOK value for each telephone you have connected to this device.
Set the OFFHOOK voltage to the lowest setting registered for all your telephones, e.g. if your
telephones return values of 4, 5 and 7 then you should set your OFFHOOK voltage to 4.
Note: The detected values will not automatically be set by the Check Level function; you
must enter the lowest level detected after testing all your telephones.
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