USERNAMES VS EXTENSIONS - Understand The Concepts

I am a new user and I was initially confused about usernames vs extensions.

The username is for webservices hosted by FreePBX, etc…and the extension/secret is the actual login/info for the SIP phone.

Correct?

The SIP secret is ONLY used to register your phone to the PBX. Your user credentials can be one of either:

Voicemail PIN/Extension number - for accessing voicemail and Phone App login

Username/password defined in User Management for access to UCP, iSymphony, etc

To add to the confusion - many instruments (including softphones) use the term “username” for almost everything, often all at the same time.

When registering a phone, you use the extension and the secret associated with it.

Almost any other time, username and password is going to depend on the “destination.”