Less of a question than a complaint (not that a mod will read this), but I find it extremely annoying that in order to apply a ringback tone to a caller, I have to enter each and every contact and each and every phone number manually. That's all.
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.