The iPad Air 2 and iPad Mini 3 come with a new Apple SIM card, and AT&T has decided to lock the SIM onto its network.

This new Apple SIM is designed to be universal and be compatible with various carriers across the U.S. and UK, including AT&T, Sprint, T-Mobile, and EE UK. Although the Apple SIM itself is universal, which means that it can work on different networks, AT&T has chosen not to support this interchangeability. Instead, the carrier is locking the Apple SIM that comes with cellular models of the iPad Air 2 and iPad Mini 3. In other words, once you use that SIM with an AT&T plan, you will not be able to use it on another 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. When you choose AT&T on iPad Air 2 or iPad Mini 3, AT&T dedicates Apple SIM to their network only," Apple explains in a support document.

"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," adds the company.

AT&T seems to be the only carrier that is locking the Apple SIM card to its network. Sprint Stores, meanwhile, will carry only iPads with legacy Sprint SIM cards, not Apple SIM.

Simply put, AT&T locks the Apple SIM for the iPad Air 2 and iPad Mini 3, Sprint and T-Mobile don't, while Verizon Wireless chose not to participate and does not support the Apple SIM on its network.

Those who use the Apple SIM with AT&T will have to purchase a new one from an Apple Retail Store if they want to use their iPad Air 2 or iPad Mini 3 with another carrier program.

An AT&T spokesman has confirmed to Re/code that customers who use the Apple SIM with AT&T will need a different SIM to use on another carrier, but didn't really explain why it chose to do so.

"With us you can change carriers with this iPad any time you want," the spokesman told Re/code. "It is an unlocked device... All [you] have to do is switch out the SIM in the device so it works on another carrier."

"It's just simply the way we have chosen to do it," added the spokesman, when asked about the reasoning behind this decision.

While AT&T must have its own reasons for locking the Apple SIM to its network, customers will most likely not be too happy about this strategy. Many may choose to go for Sprint or T-Mobile instead, but it remains to be seen.