Originally Posted by
draver
A sure way to disconnect all cellular services is pop out your sim when you sail away, then reinstall it when you dock in the next port. You'll still have full WiFi & Bluetooth, but no worries about cellular activity. Airplane mode is the easiest method, but you sound like that might not be working for you.
That'd also cause Wi-Fi Calling to stop working while the SIM card is out, which might be a problem if OP relies on it. Though DIGITS might be an okay alternative in that case.