Phone service

It's a bit puzzling that your phone wouldn't connect in Europe on your last trip. What type of phone are you using? Hopefully it's not one of the older Verizan CDMA models?

In order to use any other SIM cards, you'll have to ensure your phone is unlocked. Two solutions that come to mind.....

• try Verizon international roaming again. If you have a compatible phone, there's no reason it shouldn't work. A knowledgeable Verizon agent should be able to provide information on that.
• while you're in Gatwick, try to find a Carphone Warehouse or similar vendor. Buy a SIM there and that should work in all the countries you'll be visiting. Since it will be on a PAYG plan, be sure you get the information on how to top it up when you leave the country of purchase. Buying the SIM card there will probably take an hour or more so you could also wait until you arrive at your first country on the continent.

You could also buy a travel SIM from Cellular Abroad, Mobal, iRoam or other firms. That way it would be set up before you leave home and you'd have a working phone as soon as you step off the plane.

I've also had lousy luck using my Verizon international plan. Sometimes it works, often it doesn't.

So on my most recent trip, with a lot of help from the forum, I bought and activated a Vodafone UK SIM while in the US and used it while traveling in Germany and other countries.

You can read the details of buying, activating, adding credit and using the Vodafone UK SIM here:
https://community.ricksteves.com/travel-forum/tech-tips/vodafone-uk-sim-card-for-use-in-europe

Would not buy something in Gatwick. Brexit is end of January (plus time for negotiation) but I am not sure that the UK SIM providers ensure a free roaming in EU tariff?

Buy a SIM in Salzburg. Austria is one of the cheapest telco markets in Europe.

I have a S7...no idea but verizon didnt work in London or Scotland.

If I get a sim card in salzburg it will work in Germany? I've read varying things.

Like CWSocial, I had good luck using a Vodafone SIM card bought online, although mine was Vodafone NL (thanks Andrew!) Popped the card into my unlocked Samsung 6 at home, used it through France and Germany last year, switched back to the AT&T card when I got home. Put the NL SIM in the phone every 6 months make a text to keep the number active, then put it back in before my current trip which has included France, Germany, Austria and Hungary. €9 for 2GB of data is more than ample for me for a month and easy online topping up.

As an emergency backup, my husband has the option of using the AT&T $10-per-day plan just by turning off Airplane mode -- my phone is on vacation hold so there is no chance of running up AT&T bills.

Thanks everyone! I'm going to do the sim card with Vodafone as suggested.