I guess it all depends on the system the building is using?
My friends live in a really old apartment, their buzzers probably been installed for 4-5 years now? They use a fongo number to forward to both their cells.
I know this link isn't helpful: https://support.fongo.com/hc/en-us/arti ... ty-Systems
But it does say Although many Fongo users may not have an issue using Voip in conjunction with apartment door buzzer entry systems only Fongo home phone doesn't work properly with it
I love Witcher 3!!