I was referred to Packed8 by a coworker. He told me that he used to have their service and it worked great with minimal delay and clear sound. That was 6-8 months ago. The new firmware on their appliance is supposed to be even better with automatic updates, so it's pretty much worry-free.
I'm still skeptical. I would have considered vonage, but they didn't have local numbers in my area. Packet8 definitely is packed with features and has many extra options for cheap.