After purchasing a Ringtone through Verizon they will send you a MMS text message.  The message will be from number 000-000-000.  Open the message .  It will say something like "Congratulations! You have successfully purchased your Verizon Wireless ringtone."  Play the tone by tapping on the icon with the media play/music note. After playing press the menu key -> then select "Save Audio." 

Now go to "Settings."  Select "Sound & Display."   Select "Phone Ringtone."  Scroll to the bottom of your ringtones.  Your new ringtone will be named something like "MMS_11111dm" with other numbers in place of the 1s.  Select it and press "OK."

I renamed my ringtone with the name of the tune I purchased but it still showed in my list of ringtones with that odd naming convention the used above.