My mum has always answered the phone by reciting all 6 digits of our phone number, but the rest of us just say 'Hello?'. I think she does it to confirm the number that the caller has dialled, in case they got the wrong number or something, which can be easily done (when I was younger, my friend's phone number contained exactly the same digits as the local doctor's surgery, but in a different order, so they would often get people calling the wrong number).