I would also suggest integrating ez-ipupdate to your apps so it can be reached from anywhere. (Using a reversed ssh tunnel too would be nice).

But then again, it all depends how dumb the thief is.

This kind of idea has been discussed before here at great length. I don't remember where the thread is, though

Would indeed be nice for all n900 users

I personally think that GPS position of phone not very critical for this program. If you will have GPS position what will you do? Go to thief or go to police?

I think this program should work in other way:
1. Should check some bite in internet but only if internet connection active!!! Why? because if person will be asked about new connection he can think that something wrong and can reflash device. DON'T forget that most of thiefs don't need your data they need your device.
2. Have possibility to be activated by sms. But on which number are you going to send SMS. Your sim will be in trash bag immediately after phone will be stolen. They usually turn off phone immediately and turn on only after change sim.
3. Most important activation should be by change SIM card!!! phone should be switch to anti-theft mode if SIM card was changed! Very important information to collect is
1) New Phone Number.
2) Operator.
3) Will be great to collect all new SMS(in and out) and dialed numbers.
4) Will be great to record calls and send this records to server.
5) GPS data log
6) Photo from front camera. Photo should be made when person use keyboard. For example after pressing 5 letters on keyboard.

Very Important Phone should not be locked by PIN because in this case phone will be reflashed and your tracking software disabled. But if program will remove all contact if phone number was changed is ok. For protection private data can be used some encrypted folders which can be locked by changing SIM card (phone number or some contact on sim)

In case phone will be stolen for Police will be more helpful 1) New Phone Number; 2) Operator; 3) new SMS(in and out) and dialed numbers; than GPS data.

And one existing linux solution is here http://adeona.cs.washington.edu/

great Idea I am looking forward to this nice little app

Yea, I'm waiting for it, hope one will come out soon, cause I live in thieve's country so it's better to have one app to get phone back

I'm watching this post with interest, I recently used smartprotect on my Omnia, http://forum.xda-developers.com/showthread.php?t=464336

Is it also possible to have an application which starts a loud alarm sound after a few seconds if the phone is being touched (accelerometer status) which can stop by a few gestures (like shake left, right, left)?

Sure it is, though a downside is the app is using lot of battery by keeping accelerometer on.

These software are useless when the thief flash/update the S60 phones