Why our Apartment Complex needs Intercom ?

SHORT ANSWER:
A big complex like APR Condominiums has too many end-points of communication which need both simple calls as well as Multi-point-to-point simultaneous call handling and unlimited minutes of use. These spans areas of zero or  ineffective cellular coverage right to  acceptable-to-good cellular coverage. The only feature-rich, reliable and cost effective solution is a wired intercom system supported by a Business Grade PBX which provides supplementary services and required intelligence for handling voice calls like any medium-to-large enterprise.


DETAILED ANSWER:
Their is no one correct answer. It depends on what facilities and infrastructure you apartment complex has. Consider two extremities of the situation:

Complex A - A SMALL apartment complex (very few apartments) with NO AMENITIES

Complex B - A BIG apartment complex (like Adarsh Palm Retreat, Prestige Shantiniketan, Brigade Metropolis, Mantri Espana, etc) with MANY AMENITIES

AMENITIES imply the following:

1. Clubhouse with many recreation, well-being and sports facilities (like Yoga room, Restaurant, bar, Badminton courts, squash courts, Tennis courts, swimming pool, Gymnasium, etc
2. ATM
3. Supermarket and Grocery Store
4. Creche
5. Ironing shop
6. Dry cleaners 
7. Beauty Salon, haircut, etc
8. Medical store
9. Multiple Gates for entry/exit or intermediate security checks
10. Others like association room, Maintenance/Plumbing/Electrical office(s), Surveillance C and Security Control roooms, Telecom Service provider support offices

and the list goes on and on as much marketing brochures can fart and builder can deliver. Generally bigger properties have world class clubhouses with a long list of amenities. 

Now Complex A is a small property. The communications with the community are rather limited:

1. Resident to Resident (helper information/reference, neighbour issues, or just a social chat)
2. Resident to Security and Vice Versa [for Visitor or helper management)
3. Resident to perhaps maintenance-cum-security office [i.e. if we really have one in the first place]

Such complex has very limited number of communication points. The directory is small, easy to maintain and *always keep consistent with actual tenancy.  It is possible to store mobile & landline  numbers of each and every resident and office in mobile. And the amount of traffic of such interactions (even directed towards or from one *busy point like security gate or maintenance is very small). Therefore in such as case mobile-mobile solution is an acceptable and potentially workable solution. 

But Complex B the interactions extend far beyond the the 3 points listed for Complex A, such as

Gate to Gate (Security co-ordination)

1. Facility office to facility office
2. Clubhouse amenities to Residents and vice versa
3. Between Clubhouse facilities
4. Resident to Supermarket and vice versa for ordering stuff and settling payments 
5. Bookings of clubhouse on phone
6. Conforming medicine availability, parlour appointment, creche inquiry
7. Security calling 
8. Asking Iron guy to collect clothes or deliver
9. Security to apartment in case of any event, maintenance to apartment, apartment to maintenance for issues such as power outage, water supply stopped, help for apartment  maintenance, etc
10. Helpers to any flat or facility office
11. Kid/elder getting hurt or needing urgent medical attention. may or may not be carrying mobile or able to speak, but easier to speak flat no. and then flat no are directly mapped to intercom extensions
12. and the list goes on and on ...

Plus their is a sheer explosion of communication points like 1000+ apartment units and 50-100 common area extensions. It is very tough to load all number into 1000+ mobile phone keep, and even if its done, keep them up to date all along on all mobiles. Or worse look up in some online/offline directory and dial. For e.g., tenants and owners moving in and out and database not getting updated.  or ensuring only authenticated numbers are entered in directory, etc. These are operational headache. Multiple people can end up calling security/maintenance at same time with most getting a busy signal and having to retry periodically till they get through [Power Outage in block for e.g.] lowering user experience. Technical challenges like no cellular coverage, phone batteries failing or getting discharged fully, spotty cellular coverage indoors (typical of large residential  complexes outside core central and developed mixed-use city areas like APR or Whitefield), no signal in basement where maintenance offices are located further hinder smooth communication.  Any solution based on wireless (cellular) is simply not reliable enough. 

Therefore Telecom Sub-Committee believes that the Reliable system is a wire-line intercom system (for intra-facility communication) which can follow on mobile (resident roamed outside the apartment) if required or requested by resident either *always or *conditionally (no-answer or busy) or even *never (for eg, on holiday or business travel to other city/country)