Sorry, I don't think you're being realistic here.

How are you going to phone home if the thief or user doesn't have an Internet connection? He might have some WiFi and BT passwords but those aren't neccesary useful unless he/she lives near your WiFi APs, or also got your phone.

A car gets stolen from West Europe and 12 hours later its already out of Europe. The car at whole, or nowadays: in parts. Small electronical devices like this get stolen and resold quickly. The person who ends up with it will be a poor smuck who can't afford it new. He/she bought it 2nd hand, knowing or not it was stolen. The higher the difference between regular 2nd hand and the price its being sold, the higher the chance is its a stolen device.

A script like this is a great idea, but IMO it is part of a bigger plan. Its better to prevent a device like this to be stolen. Don't walk around with it in the big city, like a tourist looking at his/her uberexpensive GPS device, this attracts certain people. For example this weekend I've been in Amsterdam and I usually kept my NIT in my moneybelt. I have 2 good locks for my bicycle which is the minimum, I lock my bicycle always properly (2 locks, in a way pissing off the burglar as much as possible to slow him/her off), and my bicycle looks old. Also, if you expect a device to be stolen, use encrypted partitions like TrueCrypt or LUKS. Activate these during boot, and disable swap (or use encrypted swap).

There are, basically, stupid thieves and smart thieves. The stupid ones are already jailed. The smarter ones are still floating around. You can protect yourself from the stupid ones, but the smarter ones is more difficult. Therefore, while I'm not saying the feature is useless, I highly doubt the thief would use the device. The difference between a bike and a device like this is that the thief cannot know what the device is, and what its features are. He'd probably think its a weird phone (because its a Nokia). This'd also be one of the reasons the first thing he'll do is putting the thing off and getting the SIM the hell outa there. Because he or she knows about tracking via 2G cell tower. I think the first the he does is putting it off, and then figuring out how much they go 2nd hand, going a bit under the normal price but not too much so it doesn't look sneaky, or if his customer base knows its stolen he gives it for a friend price (say 50 EUR).

And, I know for sure cops don't give a SHlT about a stolen bike or mobile phone. They don't have the manpower for this, and it doesn't earn them any cash either. They write it down in their database, but nothing will get done except maybe later for profiling if the thief strikes again. The chances these people get caught are, in my country very low. IIRC less than 20%. Heck, they have a hard time jailing people dealing harddrugs while they always do it in the same neighborhood, even same places approx too.

There is another program linked to here on ITT about a message at boot up which shows whatever text you prefer like an e-mail message. Its more effective against honest finders.

Just some viewpoints.. cheers

Addendum: When setting up a defense barrier it is important to first define who and what you're trying to protect yourself from, and then implement one or more ways against this/these attack vector(s).

When I walk with my NIT I also put my left hand under it, using the thing it should stand on around my left hand with my fingers around the device on the right top. Then finger or stylus from the right hand. This way it is also harder to accidentally drop the device.

That said, I will probably use VPN + FTP + a write only directory to which the IP and current GPS data will be send to, but I would do this via crontab, and only set this on when I'd go to a risky area to save CPU cycles. Maybe it'd be useful to have some kind of authentication every X days, verifying the user is still authentic. If not, it goes into phone home mode. I'm pretty sure some proprietary software works like that