Pattrick,
The voicemail replacement is not mandatory. After installing Google Voice and launching the first time it will step you through setting up voicemail, but there's a "Skip" button. Just hit that. I have Verizon as well. I dial *86 to get to my verizon voicemail, and I dial my own Google Voice number to get to my Google Voice voicemail.
Does that answer your question? If you want to call some people with your verizon number and others with your Google Voice number, then Voice Choice can help you with that.
-Kevin