Michael Bazzell talked about VoIP on his
podcast. It was US centric so I didn't use his guides. He mentions Twilio, Linphone and Telnyx on his site.
He even has a post about self-hosted beta of an program working with Twilio or Telnyx numbers.
https://inteltechniques.com/blog/202...-sms-voip-app/
I heard that more than a decade ago VoIP required routers with good QoS, but this was in an business setting with quite congested Internet connection.