Update: "Never mind".
As of this week (June 26, 2017) Amazon has pushed out software updates for all Amazon Echo products that allows direct room-to-room calling.
Now by giving each of your Amazon Echo devices their own name (e.g. Office, Bedroom, Kitchen, etc.) you can use them as room-to-room intercoms by simplying issuing the command "Alexa, call kitchen".
I am very pleased to see Amazon add this capability so quickly and make it very simple to use.
My originl workaround suggestion:
The new Alexa Calling & Messaging service turns every Amazon Echo and Amazon Dot into a voice telephone. The free service allows you to make telephone-like voice calls from your Alexa device to any other Alexa device in the world free of charge. There is no monthly fee, no per-minute fee, and no per-all fee. You can also use the just-updated Amazon Alexa app on your smartphone to do the same thing.
Of course, this a walled-garden system - every person you wish to call must also own an Amazon Echo device or be using the Amazon Alexa app on their smartphone. This has very interesting possibilities and when the video-enabled Amazon Show device starts shipping at the end of June, video calls will also be possible.
For me, there aren’t a lot of people I know with Amazon devices that I would want to reach this way. A regular phone call, text message, or email would be fine. However, since I do have multiple Amazon devices in my home (two Amazon Echos and five Amazon Dots), I though it would be really cool if I could use this new Alexa feature to create an in-home intercom system like the classic wall-mounted units that have been around since the ‘60s.
With a little experimentation, late night testing, and helpful assistance from Amazon tech support I now have a room-to-room intercom system using only my existing Amazon devices.
How to make it work:
The secret to making this work is very straightforward once you understand how the Amazon Calling service supports with multiple devices. When you receive an incoming call, only the Amazon devices associated with that specific Alexa account will ring. When you tell Alexa to answer the call, the specific Alexa device that hears you (or the Alexa that hears your voice the best) will answer the call and be connected.
The trick to making this work for room-to-room calling is creating unique Amazon Alexa accounts for each device, or group of devices. You will have to associate a real telephone number with each Amazon Alexa account, so plan accordingly. When setting up the Alexa app it will text a one-time code to the telephone number so you’ll need to use your home phone, cell phones, and/or a virtual or VoIP telephone number service that supports text messaging if you need more telephone numbers than you actually have. To clarify: you need one real telephone number per Alexa account, not per Alexa device. If you have three Alexa devices on one account, you only need one telephone number for that account/group.
You can have multiple Amazon devices configured to a single Alexa account. This is probably what you have now if you simply bought additional Amazon Echos or Amazon Dots and added them to your existing account. Amazon Calling service will simply ring all the devices at the same time until you answer. This is similar to “simultaneous ringing” or “parallel call forwarding” that many PBX systems provide. Simply decide on a reasonable grouping of devices. For example, in our home where there are two adults, the kitchen and family room Alexas are linked to my wife’s account and the home office and media room Alexas are linked to my account.
Don’t forget that if you have Amazon Prime, you can link two adults and four children into one shared Amazon Prime account which is easier to manage and allows some of your Amazon Prime features to be shared.