According to Wikipedia's definition, "A gyroscope is a device for measuring or maintaining orientation, based on the principles of conservation of angular momentum." The key phrase is measuring or maintaining orientation, which is the exact reason an iPhone 4 contains one of these gizmos.
http://www.ifixit.com/Teardown/iPhone-4-Gyroscope-Teardown/3156/1
http://www.chipworks.com/iPhone-4-teardown.aspx