I live in Oregon, one of the areas where AT&T has enabled VoLTE. I had purchased a Verizon iPhone 6+ Back in December and I noticed that my phone was on LTE during calls. I'm using this on the AT&T network. Earlier this month, I purchased a second iPhone 6+ and I went with the unlocked model because it happened to be in stock. When I make phone calls on this new phone, I notice that it drops to 4G. I'm also using this on AT&T. Is anyone else using a sim free iPhone 6/6+ in an area where AT&T has enabled VoLTE experiencing the this? I've contacted AT&T several times now and they can't offer an explanation, I'm not sure if there is a limitation in their system or something wrong with this phone.