Electric Gates And Mobile Phones

[Suetheramble]

Is there a site that explains exactly how this method works?
I am about to have electric gates installed to protect about 50 flats and the gates can be opened by a key fob, number (on key pad) or if the owner is out the flat number can be pressed ringing the mobile phone of the owner.
Is it easy to change the phone numbers if needed. Can anyone program the keypad to accept numbers.
I would be grateful if anyone has experience of this system.