Before I leaved US, I already activated Wi-Fi calling for my device. Currently, I need to change my SIM card into another device (iPhone 6 Plus), and I wonder do I need to reactivate Wi-Fi calling again or not. Based on the description of Wi-Fi calling, I cannot activate Wi-Fi calling outside of US, so I'm really afraid if I switch my SIM card into another device , I cannot use Wi-Fi calling.