There is no need to bother with google mail or any forwarding. This is too much work, when all you need is just a basic visual voice mail. AT&T Visual Voice Mail app works great! The lack of visual voice mail on android by default was driving me nuts coming off of iPhone till I found this.
Oh, and by the way, its 100% free. You only have to pay if you want to transcribe your voice mail to text and have it sent to you.
My only gripe is whatever VVM you set up, it WILL NOT replace the default button for your voicemail. The stupid thing will STILL call voice mail the old way and ask you to enter the password. If you want VVM app, you'll have to open it from your apps menu or place a shortcut on your home screen. I don't understand, if android is so customizable, why the hell cant I imbed the VVM shortcut into the default menu? (the one you get by tapping on the phone icon from main screen)