One of the big changes with the latest iPad was the arrival of the Apple SIM, which lets customers buy an iPad and then choose with which carrier they want to use it.

Though not mentioned onstage, the Apple SIM was quickly highlighted as a big shift. It suggested to some the possibility of an exciting new future in which customers paying full price for their device could effortlessly hop from network to network whenever they want.

The picture gets a little less rosy when you consider that Verizon requires a separate SIM. The idea of easily switching back and forth among carriers took another hit when it became clear that AT&T was participating in the Apple SIM but is choosing to lock that SIM to the network once a customer uses it on AT&T.

AT&T spokesman Mark Siegel confirmed to Re/code that customers who use the Apple SIM on AT&T will need another SIM card to switch carriers, but stressed that the device itself remains unlocked.

“With us you can change carriers with this iPad any time you want,” he said. “It is an unlocked device. … All [you] have to do is switch out the SIM in the device so it works on another carrier.”

As for why AT&T is locking the SIM card to its network while other carriers are not, Siegel said that “it’s just simply the way we’ve chosen to do it.”

That said, the latest iPad is still a pretty darn open device, with a single model working with all four major U.S. carriers and some overseas as well. The ability to change with just a switch of a SIM is far more open than most devices sold in the U.S., which typically support at most a couple different options.