I am on a Warp/Verizon Shared Data plan (@$10 mo.) that does not have international roaming included. It has no option for data roaming, so the basic plan cannot roam. Therefore it defaults to “Using Cellular Data” with or without data roaming On or OFF. A minor consideration is, you can only get the IMS feature with WiFi calling enabled. That can only be enabled while in the US. If it falls off due to a carrier fault or reset, you will lose the feature until you are back in the States to reset it. I chatted with support and asked if a US based VPN could be used, and he was unsure if it would connect to set that up. They did however enable my WiFi calling remotely for my Warp line once, so if you ask nicely it is possible.