Simply put, almost all telephone services will be wireless (Wifi/Cellular), or plug into an RJ45 connection. This will allow the reduction of obsolete telephone lines. The building has 2 elevators, and both elevators are likely to use RJ11 (telephone) connections to connect to the call box. With that said, there will be a need to support these 2 points of obsolesce. The original idea was to use an ATA, but this would add to a point of failure which I am not fond of.
Instead, there will be a telephony service that would sit in the communications room. This server will have 2 FXS ports which will plug the elevators to the telephony server that would need to be acquired anyhow. This server will handle all of the communications for the building. This includes the first floor’s business, and multiple lines for the residence – all of which will use RJ45, or Wifi. There will of course be the option for cellular which should work properly (even with Wifi calling), and allow for calls.