Not sure about your specific phone but I have a Moto X and the process for that one is:

1. Tap on Settings
2. Tap on "more" under the wireless & networks grouping
3. Tap on Mobile networks
4. Tap on Network operators (choose a network operator)

From there, each available network is listed and I simply select the one for the locale where I happen to be from their list when they send me a welcome text (Unicom in the P.R.C. and Docomo Group in Japan). Of course, they may have more than one carrier from which to choose. Once the appropriate carrier is selected, it should register your SIM to that network.

Anyone have any idea what the ambiguous "excessive roaming" clause might mean? I'll be in Japan/China for a few weeks, back in the US for a few days, than off to Europe for about a month. Will I run into issues?

I believe it's 50% or greater but you should re-read your contract.

One month out of country isn't an issue.. .It's if 50% or so of your usage is purely out of country. In other words if you purchased a TMO account/device just to roam ensure you use it in the US also.

Best to ask CS. We have family plan but for my number, 90% is overseas as I don't use the phone stateside! except for long day time personal calls.

Called CS just to confirm. They said as long as you don't plan on moving abroad and keeping your line you'll be fine. Their wording (in their system) says multiple months of use outside the country. Thanks everyone ^

I signed up for this service just before leaving on our honeymoon trip in December 2013. Here's my brief review:

I went into a T-Mobile store and signed up for the “Simple Choice” plan with unlimited talk, text and data for $70/month + tax. They asked for my driver’s license and social security number; I made sure to ask if they would be doing a “soft pull” or a “hard pull” on my credit. The girl helping me didn’t have the slightest clue to as what I was talking about but I proceeded because it would have to be a “soft pull,” right? I mean, they’re checking my credit to make sure I can repay them around $100/month… Well, I was very wrong. I returned from the trip to find this added to my credit report:


My advice: Proceed with caution and be very clear with the customer service agent that you’re not consenting to a hard pull on your credit report.

Here's where I used the service:


Germany, Frankfurt: Service worked great all over the city; I was able to use Google Maps easily. I had 3G data service throughout.

Latency: 496ms 412ms 429ms 427ms 409ms 364ms 389ms 400ms 406ms 412ms
Speed: 196kbps
Latency: 1051ms 451ms 422ms 726ms 488ms 430ms 439ms 440ms 458ms 450ms
Speed: 186kbps

Indonesia, Denpasar/Bali Region: The service was spotty, at best. My phone would often switch between 3G and EDGE data service. Despite the spotty service, having the phone came in handy and the speed (when I had service) was better than promised by T-Mobile (they only advertise 128kbps).

Latency: 1739ms 5828ms 726ms 736ms 732ms 761ms 924ms 967ms 7559ms 1381ms
Speed: 129kbps
Latency: 706ms 740ms 757ms 752ms 738ms 742ms 747ms 713ms 759ms 954ms
Speed: 168kbps
Latency: 747ms 737ms 741ms 772ms 761ms 755ms 762ms 865ms 743ms 755ms
Speed: 191kbps

Indonesia, Ubud/Bali Region:

Latency: 725ms 743ms 697ms 759ms 727ms 715ms 725ms 717ms 714ms 696ms
Speed: 195kbps

Indonesia, Jakarta: Didn’t run any speed tests, but I found the service to work fine: 3G data just about everywhere.

Singapore: We had an 8 hour layover in Singapore and went into the city. Not sure what was going on, but we had NO SERVICE IN SINGAPORE. I have a quad-band GSM phone so no issues there.

The Maldives: This country is not included in T-Mobile’s free data plan so I did not test it. Current voice rates are at $5.99/min, texts are $0.50 and data is charged at $15/megabyte.

BOTTOM LINE: Communications used to be one of the most costly/inconvenient parts of traveling abroad, but, now (thanks to T-Mobile), it’s not just affordable–it’s downright cheap. The service, while slow if you’ve already been spoiled off of running LTE or 4G data, is adequate for checking email or running Google Maps while on the go. I highly recommend using T Mobile’s new plan when traveling abroad.

Also, I wasn't able to find a good map of the covered countries at the T-Mobile website so I made my own interactive one for future reference. Some might find it useful, you can find it here: http://weekendblitz.com/great-travel...p-calling-too/

If and when no service, often a reset of smartphone will resolve connection. I had that happen when I landed in Bangkok n reset my Moto G...then worked fine.

Just got back from mexico (cancun, isla mujeres, etc.). I had useable 3g mostly everywhere i went via Telcel and Movistar partners.

Just turn on your "roaming" and you should connect to a T-mob partner that is included in the worldwide coverage. If it doesn't connect to something seemlessly, chances are there are no reachable providers or it's the provider is not included in the "free worldwide coverage".

This was a good "simple choice" move by T-mob.

I just want to add that if you call "Tmobile Support", chances are you will hear a million variations of how to use it.

Just turn roaming on and enjoy.

Returned from 10 days in Peru, with coverage that was often better than what I enjoy at home. Speeds as expected, with somewhat high latency but low jitter, which made for clear (if not slightly delayed) VoIP calls. This trip was one of the rare times I found myself missing my old Bold 9700's UMA chipset, as the subpar voice quality in T-Mobile's Wi-Fi calling app on my HTC One was magnified to the point of being more or less unusable, negating the benefit of free calls whilst on Wi-Fi.

My biggest recommendation would be to try and stay on Movistar as much as possible -- it seemed whenever I roamed on Claro, speeds plummeted or the connection stopped working entirely.

Concur.

I was in SG three weeks ago and have had NO issues on two different carriers (MobileOne and Singtel) http://www.t-mobile.com/Internationa..._roamworldwide [select Singapore]. This was my 5th trip to SG since free roaming

In some cases; select manual network selection and choose one of the roaming partner networks. Automatic selection can "Stall" on some carriers and not come back with a failed roaming connection and the phone may still keep trying that carrier. ALWAYS have ability to manually select.

Side NOTE: Was in S. Korea this week and noticed Olleh/KT has better performance than SKT... Seemed SKT was data saturated to T-Mobile Olleh/KT had no issues

The latency numbers above concerned me. My experience is that you really want 350ms or lower for a decent VOIP call.

Went on long trip in March. T-mobile worked flawlessly in:
- Bangkok, Thailand
- Siem Reap, Cambodia
- Hanoi and Halong Bay, Vietnam
- Kuala Lumpur, Malaysia
- Bali
- Singapore
- Seoul, Korea
- Osaka, Japan

It actually worked better (signal wise) than most of Northern California. Speed was slow but usable.

Very happy with it. Would switch over if they have better Nor Cal coverage.

Didn't track numbers, but worked fine for me across Asia. Had a few initial issues in Cambodia, but fixed it with a reset of the iPhone

T Mobile Global data coverage
 

Have used mine in Prague, South Korea And Hong Kong with no issues at all. Saves me a lot of $$$ on my other line which is Verizon.