John564479 Just some info:
Using a vpn won't have any effect on calls/sms even over Wi-Fi (Wi-Fi calling bypasses the vpn to connect directly to Carrier servers), but if you use a VPN than the main difference is the network you're connected to won't see you connecting to grapheneos or any other servers, just the VPN server. The other thing is the captive portal check will bypass VPN too, but you're able to choose between grapheneos or Google server for that depending on your preference.