AASTRA 4224 Operator for MX-ONE User Guide - Manual (Page 66)

Assistance
Dialog 4224 Operator 66
Authorisation code
You can lock/unlock an extension using the individual authorisation
code.
To lock an extension: *76*
Dial.
z #
Dial the extension number and press.
To unlock an extension: #76*
Dial.
z *
Dial the extension number and press.
z #
Dial the individual authorisation code and press.
Contact your system administrator regarding the authorisation
code.