I am a Virginmedia customer (though it was called Telewest when I first changed to them. They have a different wiring scheme. I had one twisted pair wire to a telephone master socket and one coaxial cable which feeds my router via a lightning arrestor box. That arrangement was useful. If the phone stopped working I could report it across the internet, and if the internet failed I could phone up and report the fault. I rarely got a failure though.
A year or so ago, I was sent an adaptor which plugs into the "phone" socket and presents a standard BT socket to plug a phone into. On changeover day the router was remotely reloaded and the "phone" socket became live and I was asked to move the cable plugged into the telephone master socket into the adaptor in the router instead. When I did, the phone worked. I did plug a spare phone into the original telephone master socket and it still gave me a dialling tone for two more days then it died.
The good news is that the telephone calls are much cleaner, with no trace of a hiss or crackle, and slightly louder. The bad news is that if the router fails or there is a power cut then the broadband and the telephone both die. However, I took the precaution a couple of years ago to buy an inverter which gives me mains voltage from a car battery. The original intention was to power the central heating from a spare but serviceable 60Ah car battery kept on an intelligent trickle charger, so that in the middle of winter I would have a means of powering my gas boiler to prevent the house getting too cold. I could equally use that to power my router if I needed an emergency telephone call. So far, I have never lost the ability to phone.
The other slightly annoying feature is that the original telephone socket gave a pulsed rather than steady dialling tone if there was a voicemail to listen to. The router arrangement starts with a steady dialling tone and then starts pulsing it after a couple of seconds. If I am too quick starting the dialling I never find out if there are any voicemails waiting.
If you are in an area where power fails are likely, then I would insist on a battery arrangement for the router. I am in a reliable area and in reality I can't tell the difference between my original wired telephone and the VOIP replacement.