I've used TMobile One in Turkey, India, Armenia, Canada, and UK. And it auto connects to Mexico when I'm nearby too, all for free. Best I could ever ask from a carrier. I'm pretty anxious they're going to get bought out and cut this immediately.
That said, getting a local sim in foreign countries is nice but sometimes takes an annoying amount of work and passport scans.
That said, getting a local sim in foreign countries is nice but sometimes takes an annoying amount of work and passport scans.