I just did this with Sprint online under "My Account". Sprint gives you two options, either your full name (default) or a company name / or your first name only / or a nic name.
Very Cool. I have two phones (family shared plan) under one account. It always registers my name for both phones on the caller i.d. It says, it will take 3 hrs to register, so I hope, when I wake up tomorrow, it will work. I had them change this at the Sprint Store when I upgraded to the 4S on two occasions. It's strange how my full name still appeared for both lines. Now, it shows the revised.