Free Private Phone System (PBX) (youtube.com)
VOIP. Private Branch Exchange (PBX). Set up using apps on a phone, to use a physical phone as a soft phone. You can also just install the 3cx software on a cellphone (you don't need the 'hard phone' he uses). You can use a phone number from another country (for the phone number the call receiver sees as yours), for $1 a month. Dedicated server (which can be self-hosted if you want) is free up to 10 users. 615UKpounds up to 47 users, etc. 350k companies use 3cx.