I'm sure the HN crowd could come together and form a list of 100 ideas that are truly innovative in the phone space. However, these ideas are quite risky to bring to market.
Some ideas:
1. Super Amazing Sound playback (next level) 2. Rollable display 3. More I/O (for 3rd party ecosystems)
5. Rear display, maybe eink
6. 3d lenticular display
7. Infrared camera
8. Mesh network for sms-like relay without service