Slim - to try and provide a sensible answer to your question - the answer is yes it is a security issue. On joining a ship each person registers their phone like they used to do with cameras etc. On the declaration form they agree that should the operational need arise, then they will surrender their SIM card to ensure OPSEC. You obviously have to trust in people's integrity for this to happen, but the only time I had to do it off the Al Faw in 03, everyone saw the logic and played the game.
The biggest issue tends not to be operational needs, but when something out of the ordinary happens such as a fire onboard or something similar during a period when there has been no need to restrict comms. We had an FA2 ditch and, as someone was on the phone (pusser’s, not mobile) at the time, Yeovil knew almost before the Main Broadcast had finished……
Does this help?