If you are a visitor to the USA, you can expect TMO to be stupid and abusive.
Background · You’re visiting America. You probably do this more than once per year. You need Internet. You’re willing to pay for it.
In certain countries (my experience is with the UK, Spain, and Germany) you can buy a reasonably-priced SIM in or near the airport. For example, there are vending machines at Heathrow where £20 will get you one that’s good for a week or two. These SIMs, of course, don’t care in the slightest what kind of device you put them in.
The good part · For a visitor, TMO offers prepaid plans that are not-bad-at-all; a few bucks a day for enough data.
The stupid part · If you’ve signed up for a visiting plan, you get a TMO account you can visit on the Web. So you’d like to top it up and be on the air when you get off the plane. Except for, you can’t register a non-US credit card so you have to go find a TMO store, which are not found in airports.
How stupid is this? Well, you used to be able to register non-US credit cards. And if you did this more than a couple of years ago, that credit card is still on file and still works. So TMO actually can accept foreign credit cards; only their systems don’t let you enter one.
The abusive part · There are two cheap prepay deals; one for phones, one for tablets. Because, you see, the bits that phones use are different from the ones that tablets use.
Second, the prepay deals don’t allow tethering or portable hot-spots. (And by the way, I’m told that recent versions of Android now add the protocol bit that discloses whether tethering is in effect. Bad, bad Android!) By the way, if you’re online and you try to use tethering, you get redirected to a bonehead page on the T-Mobile web site that says “click here to enable tethering”, only it doesn’t work.
Both these practices are deeply abusive. They have no sane technical justification; evidence of a table somewhere surrounded by pointy-haired-boss types, where someone made a model that predicted more revenue if they did a few abusive and stupid things.
A lot of people visit the USA. Generally, we are willing to pay for Internet bandwidth; and probably a little more than your domestic customers. All TMO has to do is get out of the way.