So I strung up an improvised whole-house intercom with an old iPhone, an iPad, and my computer downstairs. Careful tuning on the voice activation and amplitude versus SNR settings will result in a pretty reliable whole-house speakerphone intercom system.
I’m running the standard Mumur service on a FreeBSD server. Seems to work well and compensates for the background noise of my daughter’s noise machine in her bedroom while still giving me a heads-up if she’s upset about her nightlight turning off or needing someone to tuck her in again.