Polycom RealPresence Trio 8800 with Asterisk  

Using a Polycom Phone with FreePBX/Asterisk

To use a Polycom phone with FreePBX, you must set-up an Extension in FreePBX using the Extensions Module Module. When you do so, you will select an extension number and password which the phone will use to register to your FreePBX system.
Next you must configure the Polycom phone to connect to your FreePBX system.

Configuring a Polycom Phone using the web interface
The easiest way to configure a single Polycom phone is to connect to the phone using it's web interface. When you connect a Polycom phone to your network and power it up, it will obtain an IP address from your DHCP Server (in most cases, your router).|
To find out the IP address, hit Home/Settings/Status/Network/TCPIP Parameters on your phone.
Using a web browser, type in the IP address. You will be asked to select between admin and user, and for a password. The default admin password is 456. The default user password is 123. Select "admin" and enter the admin password.

Click Settings and then SIP at the top of the page.
Then click Lines on the left side of the page.
Click on the + to the left of Identification, Authentication, Server 1, and Message Center to expand those areas.
Change the following entries. These instructions assume that you are configuring extension 100 to connect to FreePBX running on 192.168.1.100.

Identification:
Display Name: What to display in a call
Address: 192.168.1.100 or your Sip server address
Address: 100 or extension number
Label: Name on Phone LCD
Number of Line Keys: 1
Calls Per Line: 24

Authentication:
Domain: 100 or extension number *We found in asterisk here is where it reads the actual extension number. And not the Domain
User ID: 100 or extension number
Password: extension_password

Server 1:
Special Interop: Standard
Address: 192.168.1.100 or your Sip server address
Port: 0
Expires: 300
Register: Yes

Message Center:
Subscription Address: Extension#
Callback Mode: Contact
Callback Contact: *97
Then click "Save" at the bottom.

Now, click Preferences and then Additional Preferences at the top of the page.
Click on the + to the left of Auto Answer to expand those areas.
Auto Answer SIP Calls: Disable
Ring Class: Ring Auto Answer
Then click "Save" at the bottom.