NEC Aspire Feature Handbook page 101

Off Hook Signaling
Your co-worker receives Off Hook Signaling ring. They must first
place their initial call on Hold before they can respond to you. They
cannot just speak toward their phone.
You can use other options when you are trying to get through. Use
Call Waiting (page 27) to wait in line without hanging up. Or, you can
leave a Callback request for a return call (page 28). If you want, send
your co-worker a Message Waiting indication (page 85) or a Voice
Mail message (page 142). You may also be able to Voice Over (page
146) to your busy co-worker while they stay on their initial call.
1.
To send Off Hook
Signals to an
OR
extension busy on a
(Off Hook Signaling).
handset call:
95