Nope when the phone light is not on it means that BT Broadband Talk has not been setup on the hub. If it is usually lit up say it was in the morning when you left but when you came home at 6 it was off that could just mean that Broadband Talk is down.
When BB Talk is not configured in the home hub calls will work fine as they are just routed over their normal 01or 02 number therefore not VOIP.
It's really easy to set it up too, just go to
http://192.168.1.254 and on that page there will be a link called something like set-up broadband talk click on it. It will take you to a page where you put in they phone number and password they got in an e-mail and on the next page configure my router a pop up will appear telling you how it got on then the phone light should be on!