Set up a Cisco 7800 phone
Register a 7811, 7821, 7841 and 7861 phone to your phone system.

These steps cover the 7811, 7821, 7841 and 7861. If your phone system supports auto-provisioning, use that instead.
Steps
- Go to Settings → Status → Network status to find the IP address.
- Open the IP in a browser, click Admin Login, then Advanced.
- Go to Voice → Ext 1 and enter the proxy, user ID and password.
- Click Submit All Changes.
- Set an admin password under Voice → System.