As others have indicated Verizon requires a password. You can't eliminate it. You can set up another contact that can dial your voice mail and enter the password automatically but it doesn't work when you hit the voice mail notification bar. That goes to the preprogrammed (no pun intended) entry which requires you to enter the pass code.
I was hoping for someone creative to create a patch to fix this, but earlier thread way back when indicated that it was too deeply buried inside the Pre to be fixed with a patch.