If you want the same ringtone for all contacts, set it as the "default ringtone". (Menu>>Settings and Tools>>Sounds Settings>>Call Settings>>Call Ringtone - choose the one you want.
Any contact that you have specifically set a different ringotne for will use the one you set for them - all others in your address book or other wise, will use the "default".
Or am I misunderstanding what you want to do??
***Just re-read the question - but the same would apply for a ringback tone - you need to do it through your MyVerizon account though. Unless Ringback's work differently - I've never used them. My son had one though - and he set it up and it was the one everyone that called him heard - he didn't have to set up individual calls with the default tone. You only need to specify if you want something OTHER than the default for someone.