I was able to use my ipad mini as a hotspot for data in Venice, Croatia, Slovenia, Montenegro, and Greece in September. I did not try wifi calling, just data.It was connected to the LTE tower, but it was still throttled.

I'm in the UK right now. I turned on the hotspot for a couple of minutes and it was working just fine.

I found the exact opposite was true for me when I was traveling in India. On previous trips T-Mo was flaky as heck and my Fi service worked brilliantly.

Tmobile download speed at Aruba is about 5kbps. Upload around 30kbps.

The data coverage in china is unusable.

Out of curiosity, what device are you on. With the exception of some iPhone models, I think most phones on T-Mo don't support all of the China Mobile bands.

I am in Shanghai right now, and T-Mobile data coverage is very flaky. I'm using it for text messaging and maps. Apple Maps works some of the time (slowly) and does not work at all a lot of the time. I'm using Verizon iPhone 6s Plus. Phone shows 4G and is using the China Mobile network.

I've used my T-Mo 6s in Shanghai - never lost coverage. Maybe the Verizon version doesn't have the same bands so you end up on a different carrier there?

We used iPhone 4s and 6s plus. Do we have coverage? Yes. Is the internet usable? No.

Same. I have coverage. Internet doesn't really work that well. That said, unlike the last 2 days, I'm able to use Apple Maps today (Saturday). Verizon iPhone 6s Plus connected to China Mobile.

They got to have cheap prepaid SIMs over there?

Not too cheap, and their bands aren't completely compatible with most US phones. Unfortunately, it's not as easy as buying a SIM in many other places.

I switched to T-mobile as free international data was a big hook for me.

Please carefully consider whether you want to do this. My customer service experience with T-mobile was the worst I have had in almost 20 years living in the US.

They could not originate my order properly requiring hours on the phone to finally get a SIM sent. Once I activated I found their signal much weaker than AT&T so that inside my apartment or office buildings I could not get service (I live in San Francisco).
When I travelled overseas (europe) the service did not work at all and there was no ability to fix it from the road despite calls to T-mobile customer service.

After some weeks back at AT&T I am still trying to confirm cancellation of my service and understand the charges of hundreds of dollars T-mobile says I owe them. I've dealt with maybe 8 CS agents and they have been uniformly awful - unable to communicate basic information, unable to perform a cancellation or providing billing details. I am forced to resort to disputing all their charges to attempt to resolve my situation.

When you factor in switching factor in the value of your time trying to deal with this company that has genuinely awful 1990s style customer service.

I think most people who've posted in this thread have had good experiences with the free international data -- the thread is now at 101 pages.

It is true that T-Mobile hasn't had as strong coverage as AT&T or Verizon. But with Wifi calling, T-Mobile works out for me in my home and most of the places I frequent.

Customer service can be frustrating with all carriers. I use the support chat whenever I can, so I can save a log of the discussion. But the chat isn't always available.

I had good luck communicating with T-Mobile support while overseas. I didn't call, instead I tweeted them and they got back to me, even wanted to direct message with me to sort out connection issues.

The only time I've had problems with T-Mobile overseas was last July when I was suppose stop be getting full-speed LTE during their summer promo. I didn't get full speed right away in Athens but by second day I was there, it worked great.

OTOH, I've had amazing customer service from T-Mobile, far better than my experiences with Verizon. The key is to get in touch with "T-Force" (through Facebook/Twitter).