Once switched to a phone connection from the hub, all the conventional telephone wall sockets in the home cease to function. It is possible to get VM to reconnect internal extension sockets around the home to the new connection from the back of the hub so as to re-enable them as part of the switchover process. However, you need to be clear to VM that needs doing as part of the switchover.
The simplest way to use the phone connection from the back of the hub is with a cordless phone setup. Plug the cordless base station into the back of the hub and use cordless phones around the home where needed. Further info at the links below