When Apple introduced its new iPad Pro 9.7″, one of the small technical specifications the company touted prompted the most questions from readers: the new embedded Apple SIM. For context, with the iPad Air 2, Apple introduced its Apple SIM, a programmable version of a regular SIM card that allowed people to choose between dozens of carriers worldwide in an on-device interface.

This programmable SIM makes it easier for Apple to ship one device that is compatible with carriers all over the world, especially when coupled with a cellular radio that integrates most of the known technologies that the networks use all in one bundle.

But those Apple SIMs have always been removable, just like a regular SIM card, and some carriers actually program those SIMs permanently, rendering them ‘locked’ to that carrier. Now that the new iPad Pro has an embedded version of the SIM, there have been questions about what happens when that gets reprogrammed. Here are some specific answers to those questions:

The embedded SIM is deactivated on the Verizon version of iPad Pro. When traveling with a Verizon iPad Pro, you would need to swap out the physical SIM card for that of a global or local carrier.

If you buy the iPad Pro from AT&T stores, the embedded Apple SIM is used and is then locked for both domestic and international use. However, you can buy an iPad Pro from other channels and select AT&T from the embedded SIM and it will be unlocked for both domestic and international use. So, buy from an AT&T store and the SIM is locked and you’ll have to roam on AT&T’s plans internationally. If you buy from another source and manually choose AT&T, it’s not locked and you can switch carriers.

No other carriers are locked. You’re safe with T-Mobile. However, there is a block in Japan for units purchased via each of the individual Japanese carrier stores (only from other Japanese carriers) and not internationally.

If you want to use, say AT&T and T-Mobile, you can use the embedded SIM, then put in a T-Mobile SIM and that will override the internal. When you take it out, it will go back to AT&T. Update: You don’t need to take the SIM out, both carriers become selectable options under cellular settings.

That might not sound like great news, but there is one very bright spot for anyone who wants to switch carriers later. All iPad Pro 9.7″ devices have a SIM slot right on the exterior and you can put another carrier’s SIM in that slot even if the iPad Pro’s embedded Apple SIM itself has been locked to AT&T. In other words, the internal SIM may be locked, but you can “switch” carriers by using another physical SIM that you buy — the device itself is never locked.

Dodged a bullet there. The reason I felt it was good to get some specifics here is that I highly doubt this will be the last device Apple ships with an embedded Apple SIM. Hopefully Apple can negotiate with carriers to eliminate the ‘locking’ requirement altogether — but don’t hold your breath for that particular utopia.

Clear as mud, to be sure, but hopefully this brings some clarity to the matter.