I have to say that in my last few trips, I'm finding more and more people I have to communicate with use WhatsApp.

Very convenient, though I do use Viber Out calls as well.

But I just need to get a prepaid SIM with data, don't care about minutes or having to figure out calling rates in different countries.

My guess is even with T-Mobile One account international data roaming, I could use WhatsApp, for chat if not voice.

Appreciate not seeing ads and who knows how FB is mining the data. But I did have to make one reservation on this trip to Puglia where they didn't have secure online booking and wanted me to email my credit card.

Worked out much better that I could send my credit card number by encrypted chat in WA.

About 10-15 years ago, a lot of smaller lodgings would get Skype accounts for similar purposes, like finalizing booking and using it for secure communications. It wasn't a widespread thing and while people have personal WA numbers, they're not getting them for business-specific numbers.