About the volume keys as someone suggested to make them skip track.. So, press = +- volume and hold = next/prev track, how about it? Nice job so far!
it can be even simplier: volume rocker is used for track skipping only when the phone is locked and it's working as it is when the phone is in normal unlocked mode. So for example, you can skip tracks in your pocket whithout even pulling out n900 and if you want to change the volume you can open the keyboard to unlock it (or lock switch) and then use volume keys for their regular use.