>>> As a weekend project, I hacked together a physical phone, a Raspberry Pi running Asterisk and Twilio, to let toddlers safely make international calls.
Ahem. Some people never heard of immigration/emigration?
(The system is valuable for adults too, if some of your relatives live in a country which blocks Whatsapp and other voice calling apps, like Russia or China).
> I built this so kids of expats can easily stay in touch with family on other continents.
Just think of families fleeing from war or persecution. This isn't rare by any measure, unfortunately.