Here's the trick! Using Alexa as an Intercom. While it's not a true intercom it will likely meet your needs.

What I would like to see is a way for different Echo's to announce who you are looking for (paging) so the person you want would pick up. This would be important in a larger household (3+) otherwise everyone would try to pick up the call (intercom) across all of the Echo's (when you have more than two devices).

So the command would be something like: 'Alexa page Frank' and then the other Echo's would call out 'Frank please pick up' within your Echo hardware domain. Amazon are you listening??