my mates x has left him and the phone bill is still in his x's maiden name as she did not change it when they got married, when the bill comes who has to pay it. and is it his or hers responsibility to contact the phone company. he is still living at the address where the phone line is and still in her name now.
The person named on the account is responsible for payment, though I guess if you friend uses it now without intending to pay and without her permission it is technically theft. I would suggest your friend contacts the phone company to change the account holder from the date the x left..