I get three bad behaviors from HD Voice (VoLTE) on my Note 3:
1) Incoming calls don't go through
2) Cannot place outgoing calls
3) Dropped calls
For #1 and #2, it seems to have to do with the flaky LTE by my work. I work at a campus filled with nearly 10,000 engineers and techie people. The LTE here is almost unusable because of the load. When I go to make a call, it says "HD Voice" then "Failed to connect" or similar. There is -no- workaround. I end up calling on a landline.
The #3 issue I'm seeing at home as well as work. I get calls dropped, usually when I am moving from one location to another. I think the issue is getting handed off from a LTE to 3G connection. This handoff is fatal and drops the call. I get pretty good 3G where I live, and LTE through most of the house. But if I start a call in one side of the house, and move to the other side of the house I lose the call. It is extremely frustrating.