I thought the Visual Voicemail on the iPhone allowed you to access the voicemail without needing to enter the password every time.
I'm most definitely NOT a VZW employee. If a post answered your question, please mark it as the answer.
Ann154 is correct. I you use the VVM app for your voicemail you don't need a password. If, on the other hand, you prefer to access your voice mail messages via the phone app, you will have to use a password or PIN. That's a Verizon/security thing and there is no way around it.