Here is some info on the ring back when free, for analog stations there no need to set a short code, if you call a busy extension and press any key it will autocb.
Have a look here;
Ring Back When Free
Also called 'callback' and 'automatic callback'. If the user called is busy, setting a ringback allows you to hang up and wait until they are free. When set, once the busy extension becomes free, the system will ring your telephone when also idle and, when answered, call the original target extension.
Note
• If the extension called has multiple call appearance buttons, you will not receive busy until all its call appearance buttons are in use.
• You must be idle (have no call connected or held) to receive the ringback.
This feature can also be set via the followings methods. These options also allow a ringback to be set when the target just rings, often known as a ringback when next used.
• Using a button programmed to the Ring Back When Free function
If the button has status indication, it will show that a ring back has been set. The button can also be pressed again to cancel the ringback.
• Use a short code set to the Ring Back When Free function
A short code set to this function can be used to set a ringback on any extension without having to actually make a call.
• IP Office Phone Manager
This application provides the user with a button to set a ringback.
• Analog Phones
Analog phone users can set a ringback when free by pressing any DTMF key before hanging up when they hear busy tone.
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It works! Now if only I could remember what I did...
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