Just in Japan and on docomo pretty much the entire time. Even though the phone showed several bars and LTE, service was far from up to par. Very slow in general and maps refused to load. I'd see the dot showing where I was but an otherwise blank display.

I had similar problems in China, but for some reason the maps decided to work.

No issues so far in Mexico. I haven't seen Telcel used yet, though, just Movistar; maybe if I go far enough outside Mexico City?

Something I'd encourage people to do when roaming internationally is to set your phone to restrict background data transfers.

On Android, Settings > Data Usage > (three lines) > Restrict Background Data.
On iPhone, ??? I'm sure it has a setting for this.

It's amazing how much of a difference this makes on performance when you're running at 2G speeds. I was cursing at 2G speeds when I was last in London until I realized how much data was being used when I wasn't actively retrieving anything.

Thanks - it's called Data Saver on my Galaxy S9.

Yeah - on iPhones, if you have iCloud photo syncing on, forget about it.

I really hate that with the newest updates you can't reset your cell data counter. Why would T-Mobile want to restrict that?

On iOS it's Settings->General->Background App Refresh->Background App Refresh->Off (or Wi-Fi). It's probably set to "Wi-Fi & Cellular Data" for most people.

I never fiddled with those settings.

initial loading of new Google Maps tiles can be painful but once loaded, it's not too bad.

For Google Maps, be sure to download offline maps when you travel, before you leave Wifi. They load faster and they don't take data. They even work where there is no data. Note that some areas (I'm looking at you, Japan) aren't available for offline downloads unfortunately.

Android instructions:

https://support.google.com/maps/answ...DAndroid&hl=en

iOS instructions:

https://support.google.com/maps/answ...rm%3DiOS&hl=en

My iPhone 6S apparently can only connect to Movistar's 3G network now and not LTE; it was on the latter for the first few days. I'm pretty sure I haven't hit the 5GB limit yet. Any idea why that is? It's still fast enough for my needs, though, so I'm going to hold off on calling T-Mobile for the time being.

The iPhone 6s supports LTE Band 2, which is what Movistar in Mexico uses.

Even if you hit the limit, it would still connect to the LTE network but simply throttle the speed. I don't know why it wouldn't be connecting now.

Interestingly, forcing the network to Telcel results in LTE being used. Maybe there's some issue with Movistar and roaming?

T-Mobile used to publish a list of its roaming partners for each country/area, but I can't seem to find it anymore.

Currently in Sapporo with later wandering out to the sticks of Hokkaido. Docomo working fine, but I am looking at the Docomo building as I type out my hotel window, so lots of bars. Just an FYI, my wife tends to low tech but she does like to be able to move around with a way to communicate. We have a T mo hotspot, so I brought it, and switched her sim with the hot spot sim, and now she has data and sms on her phone , Moto X. Extremely easy to do (5 minutes) and adds value to the plan. I should have been patient and let the auto APN get registered, but I decided to switch the APN to

Name: RoamingAPN (This can be anything. In our example it is “T-Mobile International Backup.”)
APN: epc.tmobile.com
APN Protocol (if applicable): IPv4

It was much easier than getting a local sim. Since it is throttled anyway it didnt likely matter that i switched from the fast APN. It does have an "r" by it so I am monitoring data cost but when i used the hot spot in its native state in europe in January there were no ugly data surprises. YMMV