Although this thread is quite old, I'd like to add a little update since I came across it .
Thank you Paolo your solution is right on point!
Please also note :
Change Name Displayed for outgoing calls.
Changing the user name will:
Change the name displayed on the invoice for that phone number.
Take 24 hours to show on the outgoing name display.
It will automaticly Create a new Authorized Contact Level 2 (meaning that the person(s) you would add the name off will have partiel access to the account.)
Hope this helps !