AASTRA 4187 Plus for BusinessPhone User Guide EN - Manual (Page 36)

Call Forwarding
BusinessPhone – Dialog 4187 Plus 36
Fixed Diversion
This function directs your calls to a pre-programmed answering
position (e.g. mailbox system or secretary).
Activate Fixed Diversion u *21#
Lift the handset and dial to activate diversion.
Verification tone. You can make outgoing calls as usual. A special
dial tone reminds you that a Call Forwarding is active. d
Replace the handset to finish the procedure.
Cancel diversion u #21#
Lift the handset and dial to cancel diversion.
Verification tone. d
Replace the handset to finish the procedure.
New incoming calls will be signalled on your phone again.