Creating an extension in FreePBX is very straight forward. There are a lot options, but we only need to enter a few. We will be creating a SIP extension, most softphones and VOIP phones are SIP compatible.
Select Applications / Extensions from the main menu
Click Submit to create a generic SIP device
Enter an extension number and a display name. Display name could be the name of the person using the phone
Scroll down and choose a password (secret) for the extension and if the phone is going to be behind a broadband router choose ‘Yes’ for Nat. Do not use a simple password for the extension!!
And we’re done! Scroll down and click Submit
Finally click Apply Config. This will load the changes made in to Asterisk and must be done after updating anything in FreePBX