I've developed a finger friendly application that allows you to access your Google Voice mailbox right from your handset. Right now, it's pretty simple and just lets you see who called and when and play the voicemail but I'm planning on adding more features such as starring, marking items as read, and transcriptions pretty soon (right now it is 'read only' per say).
Under the white boxes is people's names. It cross references the phone numbers with those in your address book to display by name instead of just the phone numbers. Some caveats/requirements... it utilizes the Silvermoon project for the GUI and therefore requires OpenGL support. It will "work" without OpenGL however it will be rather slow. Also, it saves the configuration and voicemails to \Storage Card\GoogleVoice so it requires a storage card to be present.
http://gvvvm.codeplex.com/
Let me know what you think and what sort of features you'd like to see as well as any bugs.