I’ve been using the Nucleus Intercom system, and it might be perfect for you. It allows you to communicate with different rooms through a wall-mounted device with a simple button interface for talking to specific rooms. It also supports video calls and connects to your home Wi-Fi, so you can use your smartphone to communicate with any room, even when you’re outside.
Just installed this in my home. The Grandstream GXP1625 in the laundry room, the Grandstream DECT DP750 base station with two DP720 handsets (cordless phones) for the living room and bedroom, the Grandstream GRP26xx for my office, and the FreePBX/Asterisk server are all located downstairs.
Establish separate page groups for one method and two ways to reach every phone. Additionally, you can use FreePBX to perform a two-way page just between those two phones by dialing *80 and the extension.
I also opened a phone service account with Unitel so I could make out-of-state calls.