No busy tone

[fatbot]

Hi
This seems so simple but I just can't find the cause
Got an IPK2 and stations do not get a busy tone when making an internal call to a station already on a trunk call. Just get the normal ringback tone
However they get a busy tone when stations are on an internal call and a second internal call is made to either station.
Any help will be appreciated

 

[belevedere]

If they are off hook on a direct trunk line or a CAP key then their internal extension is not seen as busy, therefore will get a RNA.