I don't have any experience with using my phone as a hotspot since it's currently disabled. I may enable it at some point... 

For those of you on AT&T (or other), does your hotspot still operate when using CarPlay? Thanks.

I had an audio shop test this for me. They tested both Alpine and Pioneer head units with an iPhone 6 on Verizon. They had the hotspot on and a wi-fi only iPad connected to it. When CarPlay was in use the iPad remained connected. It was repeated a few times for validation.