Federal and State law requires that there is an elevator line within the cab of the elevator. This is in the form of a call button which will contact the elevator’s maintenance service. The elevators do not have an answer button, so I will would imagine that the elevator can initiate the call, but not the maintenance company. With that being said, there will be 2 extensions (one per elevator). The CNAM will display the voicemail number on the Caller ID information as to not need additional numbers. The only connection to telephony services that elevators has are RJ11 jacks, and RJ11 lines. There will be an RJ11 cord that would go from the elevator jack to the ATA (Analog Telephone Adapter), and from the ATA to the the network. Once connected to the network, the telephony server will handle everything else.
If a dedicated telephone number is required for an elevator, that would be simple enough to do. Each telephone number will cost $2 for a pay per minute line. Since these lines will only be used if the elevator is broke, it is not likely to ever be needed. I have yet in my 52+ years of living ever was in a situation where that call button was used.