had some old android phone and tablets. still working well. it would be a big waste if throwing out.

Found below article, convert them to pagers, put one android into every room. working perfect!, but you should have a raspberry pi 3/4 and install freepbx on it first


Reference:

https://www.cosfone.com/a-free-intercom-paging-system-with-raspberry-pi-and-old-android-phones/

Instead of wasting hundreds of $$$ for an expensive cordless phone set to put in every room (only for a single purpose), I have bought some inexpensive pre-paid android smartphones (when they were on sale under US $20) and use them as extensions to my FreeSWITCH for almost 4 years. I also use them for other communication (multi) purposes, i.e Signals,Telegram, WhatsApp, etc. The only drawbacks I can think of using this approach are inconvenience in charging each smartphone and more waste (not very significance) on electrical bill to charge the smartphones. Perhaps, a wireless charging station for each smartphone will be a plus, but this adds up to the total cost significantly?