I'll take issue with the comment that receiving a text can incur a charge - as I don't think this has ever been documented as being possible. The logic always went that with calls you had the option of not accepting/making/answering a chargeable activity. With incoming texts you have an open door of abuse if they were chargeable... back in the early days of mobile I seem to recall some dodgy middle-eastern networks apparently tried it on, but anyway... off-topic.
But bromham is absolutely right about smart-phone settings, apps etc... it is far too easy to make a mistake or miss something.... And it also doesn't surprise me that cruise lines effectively hold you hostage as far as internet access is concerned, it's not as if you've got any other option while you're at sea....
There have been a couple of posts one here from people who can't roam on to maritime networks and the two biggest don't show roaming on Virgin on their websites. They seem be confined to the main networks and not MNVO's or whatever Virgin claim to be now.
As a Very Insightful Person, I'm here to share my knowledge. I don't work for Virgin Media.