For people looking at OSS, Phoniebox seems to be the popular/mature project: https://phoniebox.de/index-en.html https://phoniebox.de/index-en.html (My partner

For people looking at OSS, Phoniebox seems to be the popular/mature project: https://phoniebox.de/index-en.html https://phoniebox.de/index-en.html (My partner and I are building one for our daughter)