I tried fax with Vonage for years. Horrible! I tried machines from every manufacturer, went through multiple "fixes" and some would work occasionally. I could usually get 1-2 pages to go through 75-80% of the time. Anything more then that would result in communication errors of some sort.

I do use Voipo's premium fax service now and am very pleased with it. Most of my faxing can be done via email now, but on the occasion I do need access to an actual POTS fax machine, their service works perfectly.