In the past, the User Agent string for all devices began with the format "MakeModel/firmware." As mobile browsers advance in sophistication, they more closely mimic PC-based browsers, and the User Agent string now begins with the browser name (e.g., "Mozilla/"). Device make and model information is pushed farther back in the string, which makes the information difficult to parse.
To simplify device detection in these circumstances, AT&T handsets now report a new header,
x-att-deviceid. This header, appearing on all upcoming AT&T devices, will report the information that you're used to seeing at the start of the User Agent string, enabling a simpler parsing field to identify a device.
x-att-deviceid header is inserted by the device (i.e., no gateway is responsible for this header). It will appear in app HTTP connection profiles.