If you find yourself unable to make outbound calls and you discover the following From line:
From: "Anonymous"<sip:anonymous@anonymous.invalid>;tag=abcdef12
You have enabled the "Hide my number" feature from the UI. Not all SIP servers and services support this; if your calls do not complete, disable the feature and contact your SIP Service provider or administrator about support.
Read more about the feature in the User Guide and learn how to enable and disable it: