Apple has released its new iPad Air 2 and iPad Mini 3, featuring the new Apple SIM which theoretically allows users to switch between data carriers whenever they want. AT&T, however, wants none of it.

If users choose AT&T as their data carrier, the company will lock down the SIM to be used only on the AT&T network.

"Using Apple SIM, you can choose from different cellular carriers and their various programs. The data plans vary by carrier. For instance, in the United States, you can choose a domestic plan from either Sprint or T-Mobile and also pick an alternate plan from the other carrier as needed," says an Apple support page. "When you choose AT&T on iPad Air 2 and iPad mini 3, AT&T dedicates Apple SIM to their network only."

It seems as though AT&T is the only company to be locking SIMs to its own network, with T-Mobile CEO John Legere indicating that T-Mobile does not lock a customer in to T-Mobile. Verizon Wireless doesn't participate in the program and uses its own SIM cards.

It does seem, however, that devices purchased at the T-Mobile store will include a SIM preset to T-Mobile. iPad Air 2s and iPad Mini 3s purchased at an Apple Store or other third-party stores such as Best Buy will not be locked to any carrier. T-Mobile maintains that it is more convenient for users to preset iPads sold in its stores to its network because someone shopping at the T-Mobile store would presumably want to use the T-Mobile network.

Fortunately, however, locking down a SIM card does not mean that the device itself is locked to a particular carrier. Users can get another SIM card to use on a different network if they want.

The issues with the Apple SIM highlight the differences in priorities between Apple and mobile carriers. While Apple would prefer to make purchasing an iPad and switching carriers as easy as possible, carriers want to keep control over customers.

Apple announced its new iPads at an event on Oct. 16, keeping rather quiet about the Apple SIM until later. The feature comes as all four mobile carries are in a battle to gain customers, with T-Mobile and Sprint engaging in a price war in an effort to become the third-largest mobile carrier.

The feature is also great for travellers, who could theoretically choose a short-term data plan from a local carrier instead of having to find separate SIM cards that work. So far, the U.K. carrier EE is the only carrier outside of the U.S. to support the Apple SIM.

A universal SIM card could completely change how the wireless market works, especially if the feature eventually finds its way in Apple's iPhone. Despite this, it's highly likely that carriers would add restrictions for phones.