Please press the menu button and then dial 9
this will show your phone IP address.
Type that IP address into your preferred internet browser on a computer on the same network as the phone and press enter to access the phone web interface.
On the upper right click the Admin Login and advanced links shown in the image below.
Click the Ext 1 tab
Scroll down to the “Proxy and Registration” section of the Ext 1 page
Change the Proxy field with the specific domain name given to you for telecommunication services.
After the Proxy has been changed click ‘Submit All Changes’ at the bottom of that page.