E-Amusement
Happy Sky was the last version of IIDX to support the old styled e-Amusement cards, as Distorted would switch to the new "e-Amusement Pass" system. A cell phone application called "IIDX WAVE" could customize the interface of Happy Sky, with different menu music options, different frames for the gameplay interface, and being able to create custom courses.
Read more about this topic: Beatmania IIDX 12: Happy Sky