VVM is hit or miss on anything other than Android phones, but there are some fixes. If those don't work for you, we're also open to suggesting Google Voice or YouMail as viable carrier-agnostic alternatives to Visual Voicemail.
I made the switch to Google Voice a few years ago, before I was ever on Ting, and I'm really glad I did. When I did eventually switch to Ting, I didn't have to make sure it was all backed up somewhere else -- I just popped my programming codes into the Ting phone and my priceless voicemails were already all there, transcribed and everything.
What phone are you unable to get VVM to work on, and which network?