[jonpurdy]

I do something similar with voip.ms (hosted Asterisk).

The intercom calls my voip number, which can be set two ways: 1) play DTMF tone 9 to let the person in, then hang up (which is a security risk if random folks at the intercom buzzed me up trying to get in.

Or 2) plays audio "enter passcode", then:

- if the visitor enters the code that I told them, it plays DTMF 9 to let them in

- if the code is incorrect, plays "incorrect passcode" and hangs up

It also sends an email and SMS whenever someone triggers the intercom so I know about it. With passcodes, I can even set up multiple passcodes to give out to various people (like Amazon, friends) and my notification will display which code was used.