@Estel

It's an arduino (Hardware platform for noobs): Of course you can connect it by USB. Its a primitive serial connection (works as client or host).
I didn't do it:
- a) because cables are not cool
- b) I am a complete noob in hardware and I didn't want to hurt to my n900 (600$) by a false Voltage on my arduino mini pro (20$).

Infra red is in every low cost accessory kit for arduino together with a infra red remote. (So its lirc and not irda: not very fast).


@Ivgalvez
Even if compass is supported by QT-Mobility-Framework:
- How do I tell to the framework to recognize my compass?
- Not all applications use QT-Mobility. (Does OVI-maps?)