In order to avoid extremely high data roaming charges when travelling, I intend to make use of one of the GigSky (or similar) eSIM data packages on my iPhone XR. All appears relatively straightforward to set up, and https://support.apple.com/en-us/HT209044 provides useful guidance, however I wanted to check the method I will need to use to ensure I do not rack up any data charges when using iMessage and FaceTime. I will select the following option when choosing the 'default line': "Use Secondary for cellular data only: You might want to select this option if you're traveling internationally and you want to keep Primary for voice, SMS, iMessage, and FaceTime. This will allow you to use Secondary for data." [My underlining] I find it strange, but this makes it clear that iMessage and FaceTime will still use the primary SIM for their data, which is obviously not what I want to happen. To change the 'source' of data usage for iMessage and FaceTime I believe I will need to change the line that uses iMessage, following these steps: Go to Settings > Messages. Tap iMessage & FaceTime Line. Select the phone number you want to use. I will have turned data roaming off on the primary SIM before travelling in any case, so no roaming charges should be incurred, however will people still be able to send my iMessages / FaceTime calls in the usual way? GigSky is data only, so no telephone number will be in place for that line. The other option would be to use other services, e.g. Skype. I will also turn off the iMessage setting "reply with SMS" to avoid any possible charges there. I also think there should be a clearer warning by both Apple and GigSky that users will also need to switch the iMessage and FaceTime 'line' if they wish to avoid data roaming charges!