@Natalie-AGL, CustomerX stated that they had Gas and Electricity accounts which does not make your reply applicable. Now I did some testing using our account. In an Australian standard phone number there is 10 digits, for a mobile it starts with 04 then has 8 more digits, for a home phone it is similar having an area code (2 digits) and then a 8 digit home number. The authentication that AGL uses to confirm that it is a mobile number is simply that the number starts with 04 and has a total of 1 ...