I'm now in Israel. The good tech news is that my US T-Mobile Simple Choice plan is working just as advertised. I'm getting 3G data and texts are working just fine (both are supposed to be free). I haven't tried voice calls yet.
The bad news is that I can't access my Verizon email. I've never had this problem before in any other country, but all the other places I used it were in Europe. Googling, I see that someone else who had this problem was sometimes able to get their email on an app. But although I can find the app on Google Play website, I can't get it on my phone here (tried two different ways).
Morals of the story:
If you have Verizon Fios, download the My Fios app before leaving home, just in case. Note this is different from the Fios Mobile app.
Never count 100% on any thing, even if it worked before. For something crucial, always have a Plan B.
T-Mobile travel plan really does work as advertised, at least in Israel.