Cisco makes two different groups of IP phone - one using Enterprise Firmware and the other using Multi-Platform Firmware (sometimes referenced as 3PCC - third party call control). Phones using MPP/3PCC firmware are relatively easy to get working with alternative PBX systems like FreePBX or 3CX.
I have several of the Cisco 8841-3PCC phones connected to a 3CX PBX sytem. The 8800 series IP phones are rock solid, and much nicer than the Cisco SPA series phones.
Find the phone IP address
Go to Settings > Status > Network Status > IPv4 Status. The phone’s IP address will be displayed.
Open the Admin Console
Navigate to the phone’s admin console: http://10.0.1.1/admin (replace the IP address with what was displayed on the phone).
Click the Voice tab at the top of the admin console, and then click the phone tab. Configure the following options:
- Station Display Name: This is the name that you want to appear in the top-left corner of the phone (i.e, “Receiption” or “John Smith”).
- Line Key 1-10: If you’re adding multiple extensions on the handset, give each one a short name (x101, x201, etc). These names will display on the screen next to the line buttons.
Click on the Ext 1 tab. Configure the following options:
- Shared Line Appearance > Shared User ID: This is the extension number, and should exactly match the extension number in your PBX.
- Proxy and Registration > Proxy: This should be the IP address of your PBX server.
- Proxy and Registration > Outbound Proxy: This should be the IP address of your PBX server.
- Subscriber Information > User ID: Extension number
- Subscriber Information > Auth ID/Password: This is the extension authorization details configured in your PBX.
Repeat this process for each extension you want to add on the phone, and then click Submit All Changes. The phone will reboot with the new settings provisioned.