Home phones, landlines and phone systems
Telstra and Optus home phone codes, and what to ask a phone system provider.
Telstra home phone
All calls: *21 NUMBER #: #21#
Busy: *24 NUMBER #: #24#
No answer: *61 NUMBER #: #61#
Telstra: call forwarding on your home phone (official page)
Optus home phone
Optus: home phone call diversions (official page)
VoIP and office phone systems
Ask whether forwarded calls cost extra on your plan, and how long the phone rings before an unanswered call forwards.