If you're pumped about using the new iPads' multi-carrier Apple SIM in the US, don't pick AT&T as your first choice – or you'll lose the ability to switch to another operator altogether.

Cupertino's marketing claims the new, flashable Apple SIM that comes in the iPad Air 2 and iPad Mini 3 allows customers to "choose the plan that works best for you – with no long-term commitments."

But it seems that's not always the case.

According to an Apple support FAQ, not only is top-ranked US carrier Verizon not participating in the Apple SIM program, but although AT&T has signed on, it has done so specifically to undermine the tech.

"When you choose AT&T on iPad Air 2 and iPad mini 3, AT&T dedicates Apple SIM to their network only," the FAQ explains. "If your Apple SIM becomes dedicated to a specific network and you want to choose from other carrier programs, you can purchase a new Apple SIM from an Apple Retail store."

Got that? When you select AT&T for your cellular data account, AT&T disables the Apple SIM's carrier-switching feature and grabs your iPad for good, and you'll need to pay Apple money to wriggle out of its clutches.

As first spotted by Ars Technica, iPad owners are warned of this fact when they go to choose AT&T from the menu. A dialog box explains, "Once activation completes, this Apple SIM can only be used with 'AT&T'. You will need a new Apple SIM if you change carriers in the future."

Apple SIMs ship pre-installed in the iPad Air 2 and iPad Mini 3 but can be removed with a tool that comes with each device.

Sprint and T-Mobile also support Apple SIMs and customers should theoretically be able to hop freely between both carriers, although some iPad owners have reported difficulty signing on with Sprint – something outspoken T-Mobile CEO John Legere wasted no time gloating about on Twitter.

Of course, UK fanbois won't have to worry about any of this. Their new iPads will also come with Apple SIMs preinstalled, but the only UK carrier that has signed on to support them (so far) is EE, rendering the question of carrier lock-in moot. ®