This technology allows people to assign extension codes to their phone number. For example, if my mobile phone number is 801-555-9864 I could create an extension code 964 that I list on my company directory (as “801-555-9864 extension 964” or simply “801-555-9864-964”).
Callers that use a valid extension code will cause the called phone to ring. Calls originating from a phone number in the called phone’s address book will also cause the phone to ring, even without an extension code. Calls from unknown callers (such as robocallers) that do not include a valid extension code will not cause the phone to ring, but instead hear a pre-recorded message and be sent to voicemail or hung up on.
People who want to use extension codes on their mobile or home phone would simply purchase a phone that handles extension codes, or, for smartphones, simply install the extension code software on their phone. (If the extension code software is running on the phone switching network, any legacy phone will work.) The extension code software answers incoming phone calls, listens for incoming extension codes, checks if the extension code is valid, and handles the call according to user settings for that extension code.