@zhengyang if your current number is a sub line of your auntie's account, then as far as Maxis is concerned you can't do ANYTHING with that number. You'd need your auntie, as the owner of the account, to do everything.

One possible alternative could be authorization letter with photocopy IC - I've done this before for helping my dad on his telekom fixed lines, don't know what Maxis policies are though.