From The Apple Wiki

This is present in the iPhone 4, iPod touch (4th generation), iPad 2 and higher iDevices. It detects movements far more precise than the accelerometer, and creates 6-axis motion sensing combined with the Compass (iPhone-only) and the accelerometer. The chip is a STMicroelectronics AGD1 2022 FP6AQ.

External Links

iPhone 4 Gyroscope Teardown @ iFixIt