SIP code lookup

The codes with their own page

• SIP 180 Ringing
• SIP 183 Session Progress
• SIP 400 Bad Request
• SIP 401 Unauthorized
• SIP 403 Forbidden
• SIP 404 Not Found
• SIP 407 Proxy Authentication Required
• SIP 408 Request Timeout
• SIP 410 Gone
• SIP 415 Unsupported Media Type
• SIP 480 Temporarily Unavailable
• SIP 481 Call/Transaction Does Not Exist
• SIP 484 Address Incomplete
• SIP 486 Busy Here
• SIP 487 Request Terminated
• SIP 488 Not Acceptable Here
• SIP 500 Server Internal Error
• SIP 501 Not Implemented
• SIP 502 Bad Gateway
• SIP 503 Service Unavailable
• SIP 504 Server Time-out
• SIP 600 Busy Everywhere
• SIP 603 Decline
• SIP 604 Does Not Exist Anywhere
• SIP 606 Not Acceptable

The full list, with the 75 codes in the IANA registry, is in SIP codes.