On the hotdesk phone dial *43, At the prompt, enter your extension number # followed by your voicemail password #. The phone will reboot and display the username and extension number. You can now make and receive calls just as you do when you use your desk phone.

Please note you need to follow the same process to log out of the phone. Once you assign your number it will stay there even if the phone is rebooted. So please make sure you log out when finished.