I'm currently in Saigon and also connect with vinaphone. Tmo gave me other carriers but none of them worked where I am. Sometimes it says I am connected with 3G or 4g, but it doesn't seem faster and usually reverts to 2g.

I landed in Hanoi and went to Thanh Hoa province... it worked perfectly on Vinaphone... even during the road trip in between.

I was in Qatar a year ago and the data did NOT work, even though it's a listed country. $0.20/minute voice and free SMS worked fine. I've not had any problems with free data anywhere else (so far).

I've never dug in to the Cellular settings on the 5s, but it appears that there are many settings which could be tweaked. I take it you didn't pursue the matter with T-Mobile? In my experience the quality of help one can get from T-Mobile varies widely, but perhaps there is some setting which could be changed to get you connected at faster speeds?

Do you know which network didn't work; suggest is always TRY the other network as in some cases some carriers are stopping data roaming (this may be existing roaming agreement on ONE carrier never included data and on another carrier it functions fine).

For support while roaming, call +1-505-998-3793

This is a free call while roaming on T-Mobile (this means T-Mobile does NOT bill for the mins you spend on this call)

This goes direct to roaming support.

I do not. I got the phone and changed to the Simple Choice plan the day before I left for Qatar, and there were some issues with getting the SIM activated, so when data roaming didn't work, I assumed that it was a problem with my SIM or account. But then it worked properly in the next country on that trip and ever since, so the issue was specific to Qatar. I do vaguely remember trying to manually select the carrier and that there were no choices and/or it didn't fix the problem, but I can't be sure. I do know now that that is good advice and try it if I have problems.

Tmobile international coverage is spotty and very slow (not even at the rate they advertise). It is almost always easier to just buy a SIM card there.

I also had weird issues (inconsistent) in Qatar and have used the service in 25 or so other countries with no problems like the ones in Qatar.

Sometimes manually selecting the carrier can help, but I have never had issues like in Qatar.

Zambia - Roamed in the big cities and a few national parks on AirTel Zambia with decent 2g speeds. Phone in Lusaka and Livingstone was 3G but everywhere else was edge. Speeds were decent enough for browsing, email and iMessage.

Updated now in South Africa; roaming on Vodacom SA, slow 2g speeds but fine for all the basic stuff. Got the same pop up message from tmobile saying welcome to XXXXX, this country is included in your global data plan.

I'm not sure how you are supporting these claims? You may want to read through this thread and I can personally attest to decent coverage and true to claim speeds in Thailand, Ireland and Vietnam.

T-Mobile roams onto other carrier in MOST if not all countries they are the carriers with the best coverage (some exceptions). So coverage is controlled by the roaming network. If you think EVERYWHERE in the world you will get 4-5 bars ; keep dreaming. Even where I live Verizon whom everyone uses as a bencmark is the pits on signal strength (1 -2 bars and drops often). Not everywhere in the world will you get 3G/4G coverage and you will failback to 2G from a network point of view. As 2G fades away and spectrum reused for 3G/4G/LTE then you will see improvements.

Again none of the roaming networks coverage is controlled by T-Mobile just as it isn't controlled by AT&T or Verizon (or Sprint)

Now if you speak of data speeds, then YES the throttled "FREE" roaming will be slow if the roaming network has high latency back to T-Mobile. ALL data roaming on ANY NETWORK from ANY CARRIER means packets go back to your home carrier. That backhaul interconnect can sometimes as I said be latent or just not be the best (just as regular backhaul internet traffic can be). Meaning you may never burst to the 128Kps consistantly.

Suggest is pay for a high speed package or use a local SIM as you suggested. The fact that you get ANY data for free is entirely foreign to Verizon or AT&T in their plans. Get it's slow but for most of us it's MORE than usable

I'm n:confused:t sure where you've used it but I've foud it perfectly usable for everything I need while traveling. This includes use of applications like Google maps for navigation. The price is right, too!

I agree on all counts. Except for my no data experience in Qatar, it's worked more or less problem free everywhere else I've been. I've found it plenty fast enough for all of the typical things I do, other than downloading or streaming media files. That is: web browsing, app usage, email, Skype (voice), and Google maps.

The one thing I do run into problems with is downloading new apps. That takes way too long in most cases. Fortunately, it's rare that I need to do so while traveling internationally, but occasionally I stumble into a situation where a new app comes to my attention that's useful in the moment. Other than that, the free 128kbps data is just fine.

How could buying a local SIM be "easier" than doing nothing other than turning on your phone and have it work in a new country before your airplane even gets to the gate?