The thin and light iPhone Air does not have a physical SIM slot, and is limited to eSIM-only operation. That's something of a problem, because in China, carriers have not traditionally supported eSIM for the iPhone even though it's widely used around the world.
Until now, iPhones sold in China have always had a physical SIM slot, and that's still the case for the iPhone 17, 17 Pro, and 17 Pro Max. There wasn't space for a SIM tray in the iPhone Air, but China won't have to go without. Apple was able to work with China Unicom to bring the iPhone Air with eSIM to the Chinese market.
On its website in China, Apple says that customers will need an eSIM-supported carrier and mobile plan to use the iPhone Air. The company also clarifies that not all carriers support eSIM, and that customers who want to use the iPhone Air will need to sign up for a plan with China Unicom. As of right now, China Unicom is the only carrier that supports eSIM.
China has a requirement that links a user's ID to their cellular phone, something that's harder to do with an eSIM over a physical SIM. China Unicom customers who buy an iPhone Air will be required to visit a China Unicom retail store to verify their IDs with store staff and activate their device.
Apple has a support document on the iPhone Air in China that further says only the model A3518 iPhone Air will be able to be activated via eSIM in China. All other iPhone Air models, including those purchased outside of China, will not be able to install an eSIM profile from a China mainland carrier.
Chinese customers who have an eSIM-capable iPhone Air purchased in China will be able to activate an eSIM from a local carrier when traveling, but eSIMs from non-China mainland carriers cannot be installed while located in China mainland.
