We figured out the RFID bit!

As usual,you can find everything you need to build this on the internet.

Here's a very fuzzy video of it in action: 

This in not a brute forcer yet. My tag had the data on it just printed on the back.

It was just a matter of  transforming from decimal to hexadecimal and pasting that in the arduino code.

edit: I own the intercom and tags. Please don't do this if you are not permitted.