Waiting a while after dialing didn't work either. I had to end up calling ATT and they said that my specific unlimited LTE plan didn't happen to have visual voicemail on it. They added it on (no charge) and I got the visual voicemail working instantly.
As for the APN, however, it didn't work for me. Like others, I get the 4G symbol but no connectivity. Probably because I'm in an LTE area. When I switch to the VV apn, the data symbol goes away for a second, then comes back as it switches packet data to the VV apn, but that's it. No connectivity. I even get those little amber semi-circle symbols or whatever you want to call them that hover over the 4G symbol, which makes me think that there is connectivity, but facebook/internet/speedtest, none of them work at all. Anything else I should try? Or is this pretty much my being in an LTE area?
Samsung GSII Skyrocket w/ PACman JB 4.2.2
HP Touchpad 32GB JB 4.1.2
HTC Inspire 4G, HTC Pure/Topaz (Dualbooted WinMo/Android), HTC Fuze/Raphael, HTC Diamond, HTC Tilt/Kaiser, HTC Startrek (Cingular 3125) HTC Hermes (Cingular 8525), HTC Wizard (Cingular 8125), Cingular 2125, Cingular MPX220, Cingular MPX200, Siemens SL55, Some other old Siemens, Some old LG, Nokia 5190 as my first cell phone!