The list of extensions defined for the selected tenant are shown along with the Number, Name Description, username and password associated. You can change or set the password as per your convenience. If you change the password then make sure phone or device need to configure with the new password.
For each extension a small icon on the left will display the status: green for registered, red for off line, yellow for not registered yet.

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How to change the CLI for extension (Caller Id shown to user) 

Select Extension -> go to Outbound Calls -> select the DID number from External CID Number listè Click on Save Button.

 How to activate Missed call alert on particular Extension

Select Extension -> go to Additional Destinations - Active if checked section -> Enter your e-mail address in Email missed call notification to: field.

Please note that if extension is included in Huntlist or in Queue then call answered on other device also generate the missed call alert as you have set it for your particular extension.

If you set missed call alert on extension level say for ext 301. There is huntlist for Ring All  (301, 302, 303). Now if call not answered on 301 then missed call alert will be generated even though it get answered by any the extension 302 or 303.