How to use a custom Access Point Name profile for cellular data access
If you're an enterprise administrator of iOS devices, your Access Point Name (APN) might not work in iOS 9 unless you update your devices to iOS 9.0.1.
You can define a custom Access Point Name (APN) for cellular data access using either of two different configuration profile payloads – APN or Cellular. Only the Cellular payload works in iOS 9.0, but both payloads work in iOS 9.0.1.
If you have a profile that uses an APN payload, you should update your device to iOS 9.0.1 to maintain cellular data access.