The home phone call feature zones aren't geographic, but based on the hardware your home phone runs on. For the older landlines there are several different types of TDM switch hardware depending on which cable company your area used to use.
However all customers on 21CV are in the Purple Zone for phone features.
********************************** I work for Virgin Media - but all opinions posted here are my own
As someone with an over the top voip setup. I would question why anyone would want a VM telephony solution.
To put my system into perspective. I have 2 Sipgate basic circuits. Plus a 3 line Sipgate trunk that costs £5 per month. The basics cost nothing. Then there are of course outgoing call costs.
I connect all to a pi running freepbx. I work from home so one basic and a trunk line are assigned for work calls and fax. A second basic is assigned for the house.i have sip phone in the office a second in the house. All household mobiles also run SIP.
Meaning anyone calling the house get ivr directing to my wife or I. Even when mobile we still get the calls etc. To the office the ivr offers sales service development etc.
The best part was at one time I had numbers in three local towns. Meaning for a small business, it made me look bigger as customers would prefer to call a local number and not an anonymous mobile etc.
Also far easier to call between office and house and to be able to transfer the calls etc.
21CV is not a technology, rather it's a programme that migrates the telephone network from PSTN to IP. PSTN is circuit switched and part of the migration involves replacing the TDM switches with IP voice switches.