I believe HD calling cannot handoff from being on 4G LTE to a tower that isn't LTE. So if you're driving or at a fringe area where your signal swaps back and forth, it would drop the call. I would suggest turning off HD calling for a bit and see what happens. But yeah, that's a bad issue to have when you should be able to be happy with a new phone. I had a major issue when I got my S6 and activated the new SIM. Loooooong story short, no CS rep could diagnose it. But I ruled out handsets, SIM cards, and cell tower issues. It must have been in Verizon's system side. I hope that's not what is happening to you. But I don't think I dropped calls. I would just have people call me and it not ring for me (and go straight to VM for them).