As wylie notes, there are hundreds of thousands of these.
Ive worked with Linear and Door King
You have a 'directory access system' at the main entrance, like this:
Ive installed a few of these. Last one was like 1500+/- for the box, just to set $$.
You give it power and a phone line. Add an electromagnetic lock actuator to the main door.
IN FACT, you can add a 'cellular card' to it, in the event there is no phone line locally. (Note you will pay $80 a month to service it, if so)
Now, anyone walks up and either (1) enters a code for themself, door opens or (2) looks up the tenant name and presses "Call". The DK box will call whatever number you have programmed for
that tenant. I program land lines and cell numbers.
As stated above, the phone rings, the tenant IDs the person, and presses "9". (or whatever number you set) Door opens and the call disconnects
All well and good.
HOWEVER- if OPs local regs state that there MUST be audio access to THE UNIT, they may not accept a cell access. They may say "the point of this system, in our regs, is not 'convenience'...it is 'safety', and we require a fixed annunciator in each
unit, period".
So OP may indeed need a fixed SOMETHING on the wall in each unit. OP, you should clarify. THIS QUESTION IS THE KEY ISSUE TO YOUR SOLUTION. Doorking will work with cell; butteryflymx will work w cell.... call the inspector and ask (then get it in writing)
Changing gears a bit:
Finally, if there is conduit run with each fios service to each apartment, you can run in a low voltage telcom wire to each. For telephone, or some other local intercom system.
Note that what ive specifically described here is a TELEPHONE access system- it wont work without telephones.
If you want a system that isnt telephone, or doesnt use the telephone
company, maybe there is a PBX-type system...where each apartment gets an EXTENSION, say #1-20..and the look up at the front door then rings an extension. The extension can be just a 'buzzer box', button and ****** speaker in a 4x4. Old school but maybe cheap?
HTH