I have a setup where a user have a remote coverage path to his mobile phone. this works fine until recently i found out that whenever the trunks(analog trunks) are all used up the caller still hears a ringing tone while the system handle the calls.

is it possible to have busy-tone instead since all trunks are used up.
G450/8300 Combo running on 5.2.1

queue length is set to zero
Keep Held SBA at Coverage Point? n
Maintain SBA At Principal? n