I use the N900 only as a computer. I have a sim card in it that only does data. Thus when I have wifi access there is no reason for the cellular subsystem to be on and drain battery. On the other hand when I am out, I want to be able to connect to 3G data.

I have cell-modem-ui installed and I switch to tablet mode when I am home but I am looking for a more automatic solution.

Short version: I want cellular to turn off every time wifi is connected.

Any pointers to where should I begin?