They will not let you make changes on his account. He has to do it.
If he contacts them and asks for your name to be put on the account, they may do it but I never tried that myself, so I don't know their policy.
You could always open your own account under your own name. Ever think of that? They seem to be pretty liberal with first time buyers so if you are of legal age and want an account they will probably give you one. Otherwise, they have prepaid plans too.
