[mitchellh]

I don't think you read the article so I'll help you out. Here is how to fix the visual voicemail issue, right in the last paragraph:

"Worth noting is that some users have experienced trouble with their visual voicemail following this procedure. If you do have trouble accessing that feature, simply navigate to Settings → General → Network → Cellular Data Network and within the Visual Voicemail section add “acds.voicemail” into the APN field. Once that is done, you will be able to once again use your visual voicemail."