Corporate ?

OK - what I figured - corporate high speed rate plan

Yep.

Just did a speedtest on LTE and my upload speed significantly better - 5mbps now.

Backhaul from Taiwan networks isn't very good - so the limiting factor is their peering back to US destined traffic

Experiences from this week. Had an iPhone 6 with T-Mo SIM on $25 on ONE-PLUS promo international plan. Planned to use device for Navigation and to tether to my laptop and others iPhone. Tether was useless, since ping rate was so crappy, I couldn't even pull down a weather update.

UAE, du- Connected to LTE and 3G. Speeds were from .05-.25 download, ping times were terrible at 700-1500

South Africa, Vodacom. Got speeds on device of .02-.20 download, ping times were awful 800-1800.

Worked ok to send / receive iMessages / SMS texts. Tether was a joke, couldn't even get a web-page to load on a tethered laptop or iPhone. There was no-way emails could be pulled down over tether.

I downloaded offline Google-maps and used Navigation more than anything else to get around.

Overall it was just okay, if you need quicker data, I'd suggest a local SIM.

I find Google FI usually to be better in most places (faster) but I do sometimes use T-Mobile. Neither has covered all the countries I have been to in the last six months (Palau, FSM, Samoa (sort of) are examples) and it usually makes more sense to have a local SIM card.

Tethering isn't supported internationally, so that shouldn't be surprising. I mean, it 'works' in the academic sense, but I don't know why anyone would think tethering to a 256kbps connection that has to proxy back to the US for everything would be a pleasant experience.

I tethered my iPad to my iPhone in Spain last week.

Not optimal but works for Safari and Mail.

It's something that T-Mo advertises. Sounds like both lines get same 256k speeds right? So what does the add'l $25 really get besides stateside calling?

What additional features do I get with T-Mobile ONE Plus International?
You get all of the features of T-Mobile ONE Plus with two added benefits. Get stateside international talk and unlimited 4G LTE mobile hotspot for just $25 a month when added to a T-Mobile ONE line.

What kind of speeds did you get?

About the same as directly on the iPhone itself.

I'm not saying it was fast, just comparable to a good dialup back in the good old days.

The additional $25 doesn't really give you much of anything beyond stateside calling and unlimited GoGo wi-fi on supported flights. The plan does not include unlimited tethering internationally, only in the US. (The non-International One plan limits you to 10GB of high-speed tethering.)

Also, if you scroll down to "Connectivity, like never before" on this page, there is that sneaky asterisk next to the tethering indicating that it's domestic only.

If they do the same promotions as last year, when they gave full-speed roaming in Europe last July and August, then people won't care about upgrading to the One plan.

The One Plus plans do NOT give full speed at all

They don't currently, but last summer there was a promotion they ran called "Summer Unleashed." It provided unthrottled LTE across most of Europe.

This is my holy grail. I'm currently using Project FI (wife is still on T-Mo) for this very reason. If T-Mo ever makes this available to the masses I'll be back in a heartbeat.

My corporation is BYOD... so while we have discount codes, we don't have unlimited high-speed globally