I've never used Google voice but have heard nothing but great things. I've use Youmail which has a visual voicemail option but haven't used that in over a year either
Update. I downloaded the training ppt from htcchampions.com (dont think it's public) but there is visual voicemail and it can be accessed through voicemail or messages. gonna have to try this out cuz I dont get many voicemails
Edit: I tried it and right now it's still my normal VM but when I go in to work I'm going to check and see if there is a VVM option to add to the account like there is for iphone and BB's.