Forward unconditional can be used to immediately redirect your calls.

By default this function is only applied to incoming external calls to you. However, if required internal calls and or hunt group calls can also be selected.
When enabled, all calls matching the settings are forwarded to the number set as your forward unconditional destination. That number can be internal or external.
You can still use the phone to make outgoing calls. When you go off-hook you will hear broken dial tone.
If you also have forward on no answer set, if the unconditionally forwarded call is still unanswered after having rung for your no answer time (default 15 seconds), the system will redirect the call to your forward on no answer destination. Note that this is not always possible for calls that have been forwarded to an external number.
If you also have voicemail enabled, if the the forwarded call is still unanswered after having rung for your no answer time (default 15 seconds), the system will redirect the call to voicemail. Note that this is not always possible for calls that have been forwarded to an external number.
D = Diverting (Forwarding) Calls
A D is shown after your extension name on the phone's idle display when you have 'forward unconditional' enabled.