https://www.frequencycheck.com

Check your phone and carrier before you go.

I'm guessing any modern smart phone can do at least GSM 900MHZ, which is what you need in much of Europe. If that's all the phone has for data, then internet would be pretty slow but probably usable, because it would be limited to only very slow 2G "Edge" networks.

My phone is a Samsung SM-G360V. How do I look to set a phone to gsM? Anyone know?

We were getting 4G LTE service in much of France and Spain this past June and July, a lot of it clearly marked 'T-Mobile' as T-Mobile Germany has increased its coverage, including Bordeaux, Bayonne, Biarritz, Saint-Jean-de-Luz and all of Paris. It was also available in Donostia (in most parts of the city), Pamplona, some parts of Burgos, with good coverage in Madrid.

I guess if you're still into buying old mobile phones and SIM cards ...

Robert, even though your US T-Mobile phone always connects to the fastest 4G networks in Europe, that doesn't mean you are getting 4G SPEEDS. T-Mobile throttles your data down to 2G speeds while roaming internationally. You usually won't notice this unless you try to stream a video or something. For email and other things not requiring a lot of fast data at one time, you'll rarely notice the slowdown. I did occasionally with my 4G phone but only in a few cases.

Yes, there are T-Mobile subsidiaries operating in different European countries. They are related to the US T-Mobile but not the same company. But that's kind of irrelevant, because T-Mobile has roaming agreements in many countries where there is no T-Mobile subsidiary operating. It shouldn't matter at all whether or not you are connecting to a network that is called "T-Mobile" or not while roaming as long as it works. I used my phone with T-Mobile last year in Lithuania, Latvia, Estonia, and Russia, and I connected to 4G networks in most of them - none of them a T-Mobile subsidiary.

If your phone and plan qualify you can use Verizon's plan as a fall back but you have to sign up before you leave. https://www.verizonwireless.com/solu...tional-travel/

The SM-G360V has GSM 900MHZ, according to this:

https://www.phonegg.com/phone/5376-S...Prime-SM-G360V

but FrequencyCheck.com claims it won't work in France. Could be, but that's surprising. The phone came out at the end of 2014, so it's really not that old. Even my cheap Verizon Moto E will work over there. Still - you obviously tried to use it once before. Maybe it is time to get a new phone.

Looking at the FrequencyCheck website again, checking other phones, I want to amend my reply above to say that the SM-G360V probably could be made to work in Europe. FrequencyCheck claims that phones I own that I know will work over there will not. (It claims the Verizon phone I used on T-Mobile's network for over a year will not work on T-Mobile - obviously not true.) The other site I was looking at above claims it really does have the GSM frequency it needs to work in Europe.

You might try installing an app called "Mobile Network Settings." This free app will let you access a few extra network settings on the phone. I tried it on my Android, a Sprint CDMA phone. Obviously I can't try this unless I go overseas a again - but the setting I'd want to change would be "Preferred network type." On my phone, it was set to "LTE (recommended)". I'd try changing it to "Global" when in Europe. This should let it connect to GSM networks. When I set it to "Global" here at home, there's no difference - I'm still connecting to Sprint's network...

So, it might be worth taking that phone with you to France, buy a SIM, plug it in, set the network mode (after you've installed that app) to "global" and see if it works. If not, buy another phone over there!

If you buy a French SIM card, you're going to have to register it. That will require showing your passport to the vendor and having the number entered into the registry. Just so you know ahead of time...