Apple included a very consumer-friendly item in their new iPad Air 2: the Apple SIM. As designed, the Apple SIM lets iPad owners switch cellular carriers without going into phone stores or having to get any new parts. But in reality, mobile carriers are doing their best to prevent any actual real-world consumers from doing so.

The CEO of T-Mobile, John Legere, took to Twitter this week to talk about the Apple SIM and why it’s not really working out just yet, the Verge reports.

But what even is Apple SIM?

Modern mobile devices have a removable little chip in them called a SIM card. The SIM card is the part of the phone that actually lets it work with the carrier’s network. It contains your subscriber information — like your phone number — and gets you connected to the right 4G LTE network when you use data or make a call.

In theory, users can swap SIM cards among devices and maintain their subscriber identity. Get a new phone? Pop the SIM card out of your old one, and into your new one, and carry on as before. The system, as designed, creates a high level of flexibility and mobility for consumers.

But SIM cards do face one strong restriction, and that’s by carrier. For consumers in the U.S., if you buy a phone at a Verizon store, for example, then it comes with a SIM card that only works for Verizon. If you take your phone and switch carriers, you’ll have to get a new SIM card from your new provider.

Of course, by this point consumers are more or less used to upgrading our phones every couple of years, or to switching handsets when we switch carriers. So the majority of customers don’t think about the SIM cards in their phones that often. But phones are far from the only devices that can use mobile networks — and that’s where Apple comes in.

Every iPad on the market (each iterative generation, and each storage size in that generation) comes in two varieties: one that only has wi-fi connective abilities, and one that has both wi-fi and cellular abilities. Versions of the iPad that connect to cellular networks require SIM cards, just like phones do.

With their newest iPad, the Air 2, Apple tried something new: selling it with a pre-installed Apple SIM. As Apple describes it:

The Apple SIM gives you the flexibility to choose from a variety of short-term plans from select carriers in the U.S. and UK right on your iPad. So whenever you need it, you can choose the plan that works best for you — with no long-term commitments. And when you travel, you may also be able to choose a data plan from a local carrier for the duration of your trip.

International travel is usually a SIM-card swapping adventure that can let an unwary user rack up major data expenses, so the Apple SIM sounds like an elegant solution for iPad owners. Unfortunately, it’s already not working as intended.

The Verge collected a series of tweets from T-Mobile CEO John Legere as he explained some of the issues.

For starters, Verizon refused to participate at all. Apple’s website lists four carriers total, and the three that operate in the U.S. are Sprint, T-Mobile, and AT&T. (The remaining carrier is in the U.K.)

Verizon is still far and away the largest mobile provider in the country, with over 123 million subscribers, so that already puts a major crimp in the plan. Still, that leaves AT&T (116m subscribers), Sprint (54m) and T-Mobile (50m) in play. Taken together, those three companies’ subscriber bases outnumber Verizon’s and so Apple SIM should still face smooth sailing, right?

Not so much. As Legere tweeted, and tech sites confirmed, AT&T isn’t playing along with the spirit of the thing, either.

iPad owners who activate their new Apple SIM on AT&T will see their card locked to the carrier forever. An Apple SIM locked to AT&T is, functionally speaking, an AT&T SIM. Want to swap away from AT&T? Too bad, so sad: you’ll need to get a new SIM card from your new carrier just as you would have needed to before the advent of Apple SIM.

Not only that, but if you do initially activate your Apple SIM by connecting to either Sprint or T-Mobile, AT&T vanishes from your list of future options. So if you want to switch carriers, you can only flip between Sprint and T-Mobile.

So while the Apple SIM on paper sure seems like a great idea for consumers, for 239 million American mobile subscribers its functionality is already non-existent or heavily crippled.

Then, as Legere’s tweetstorm continues, there’s the matter of even knowing if you have an Apple SIM.

If you buy an iPad air 2 from the Apple store, it comes with an Apple SIM. However, if you buy the tablet from a mobile carrier — say, if you pick it up at the AT&T store — it may come with either a locked Apple SIM, or a provider-specific SIM, depending on which mobile company you buy it from.

When Verizon and Sprint sell devices, the tablets have those companies’ respective SIM cards pre-installed. No Apple SIM for those customers. AT&T and T-Mobile, however, sell devices with the Apple SIM — but it’s already pre-configured to those carriers. (However, cards configured to T-Mobile are not permanently locked in the way that cards configured to AT&T are.)

And as if that weren’t already complicated enough, Legere also points out that due to a technical restriction in the way the Sprint network actually functions, an iPad Air 2 sold through any of the other three carriers will not work on Sprint’s network — even if the Apple SIM in it has not been configured to any of those other networks.

Legere’s last observation? “Bottom line… it’s complicated… and it is an emerging change in the mobile ecosystem that we will have to figure out as we go.”

That’s certainly true. In the meantime, consumers will have to wait a while until the mobile carriers do figure it out before they can get the network flexibility that Apple promised.

T-Mobile CEO John Legere takes to Twitter to explain Apple SIM’s growing pains [The Verge]

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