Simple definition
SIP 480 reports that the called destination is temporarily unavailable.
Purpose and use
SIP response 480 indicates that the destination is temporarily unavailable for the relevant request.
How does it work?
It can originate from an endpoint or infrastructure that currently has no usable destination for the user.
Example and verification
To establish the cause, inspect the response origin, registered contacts, calling rules and destination state.
Points to watch
The code does not always mean a powered-off phone or incorrect password. An intermediary can map multiple conditions to this same result.
In short
Treat 480 as a result indicator requiring context from the call sequence and available location information.