IP to IP Voice Calling to another phone on Local Network

I am trying to provide similiar functionality to traditional Key Telephone System.

Using VVX411 or 501 series phone.

Here is version info on the 411

Want to URL dial between two phones and have the phone called auto answer so they can reply without touching their phone.  Turning the Auto Answer feature on the phone does not solve the issue as we can't have all SIP incoming calls answered.

I see a setting under auto answer that leads me to think you can auto answer for "Internal" Calls

Have tried to setup line as unregistered and then made entry in contacts to URL dial.

However, it just says URL dialing iw disabled.

Is it possible to accomplish this Auto-Answer on a IP to IP call?