VoIP Phones - Protalk

SIP parameters

Here are the settings used, in our case the username happens to be door, but if using AASIP then the username will be the full phone number.

SIP Parameters on a Protalk door entry phone

Then, under the Memory Numbers page, you set the number that the phone will dial when the button is pressed - it's best for this to be a Number that rings a group of other numbers.