stevehuff,

Which model iPhone are you using? The 13 & newer will work for what you are proposing as far as I know. Your Verizon line in the voice position should allow that line to switch off "Automatic" under Cellular-VZ line-Network Selection, to OFF. If nothing changes after the Auto is switched OFF, try turning ON Airplane Mode for 5-10 seconds, then OFF again. This triggers a carrier search again. You then need to select a carrier from the list that appears in a few moments that will not provide any service to the VZ line. After a minute or so that line should switch in the status bar to "SOS Only", then "Using Cellular Data". At that point it is using your Orange data service as a pseudo WiFi network for calls to and from US numbers without charges. That is, if Verizon permits those international calls for free. I use T-Moible which has free WiFi US number calls from international locations.

I have been using a US Mobile service on the VZ network and it works great under this setup. I was recently in Asia for over 3 weeks and used it for many days and 12-15 calls to the US and other locations with no charges.