So I've got an interesting and a bit of challenging problem here. My wife recently moved from London to the US. She purchased an iPhone 6s from the Apple store and has been using it with a Vodafone SIM card in London with out any issues. The specific iPhone 6S model is an A1688, and from everything that I can research is the same model Verizon would have provided.
The plan was to get a Verizon SIM card and just add her to my plan as a new line. We and two separate Verizon stores did the checks of the IMEI and other information to see if the phone was compatible with the Verizon network. All checks came back good and that the phone would work. However, when we put in the Verizon SIM card there is an initial several seconds that it appears that it will work and then it goes to NO SERVICE. We looked into things a little more and when you go to the "Cellular" option, "Cellular Data Options", and then "Enable LTE" Data Only is selected. When you try and select "Voice & Data" it brings up a prompt that says "Cannot Activate LTE Calls" and gives you a link to the following page: Wi Fi Calling "Cannot Activate LTE Calls" error message | Verizon Wireless
I did some more testing last night and wiped the phone. Upon my surprise after wiping the phone it was showing signal and connected to the Verizon network. However, when I moved to the "Activation" phase of the phone it loses signal and then says No Service. Check out the video below. I'm not sure if there is any additional activation or configuration that is needed from Verizon. If anybody has any suggestions or input it is very welcome!
iPhone 6s Activation Issues - YouTube
Thanks
Josh