I have been using 3-way calling since I've had this phone (2014). Suddenly it hangs up when I try to add a third caller!
I've been using other apps that rely on this feature (karaoke and other music apps). Their tech support says it's a known Verizonwireless issue. VerizonWireless tech support says it's not a known issue. I tried everything. I resetted network settings a gazillion times, turned phone off/on, made sure I had the latest iOS, updated all music apps. Same problem!