When the phone is lost, it's gone. As I revealed I was involved in a GPS Locate system engineering team, we didn't worry about the actual roaming on/off area. WHY? Because when the thief gets the phone they try to use it and the locate happens.
I'm guessing you are not aware of the studies done with lost phones. Maybe you don't care and demand your answers and it does not help at all if we chat about this. If so, you have your answer about if you can buy the Samsung. They don't talk to you so why buy it?
-> Here's one of many studies about the lost phone and what happens.
At the office we travel overseas and for us, the roaming issue is not an issue as we pick up a sim card or a cheap phone while we are there. However there are folk that want to use their phone just like they do in country and those tend to be the ones that think there is a problem.