Thank you everyone. I am pretty pleased with your reactions, they are all so kind and positive.
Now I hope some developers will get their hands on it and improve it.
Just a word about the development :
I got this phone about the end of september, then I started analyzing into IDA some programs, line GrandPrix*CameraTest.exe, camera.exe, Admin.exe, LCDTest.exe, etc...
I ended up reading backlight sensor, switching on/off flashlight, reading acc sensor, capturing data with front camera, with IOCTLs, or registry hack (front camera), that was so fun. Then I took the Direct3D sample, and modified matrices with acc sensor values, and I got that banana cylinder "fixed in space", cool but completely useless.
I showed the stuff to my friends and coworkers. One of them suggested to dial by gesture, the other - FX as credited in the app - the WMP plugin. The last one was easiest to implement, and with his great help and constructive suggestions through the whole process, I managed to make ShakeIt.
Apart from this, we found this project :
http://wiigee.sourceforge.net
I think there is something to do with this library and the i900 !