Many service providers silently fail to deliver SMS when one is roaming internationally, especially if not on a post-paid account
I think this must be a US thing, never heard of it in Europe.
Probably opted to buy a local SIM instead of using the one from his home country
Many service providers don't support roaming at all - especially on pre-paid accounts.
He doesn’t have international roaming.
I'm not sure that there is a subscription in Europe that doesn't include international roaming. At least I can't remember seeing one here in Norway. I suppose Europeans travel from country to country a lot more on average.