Hi there,
I built a mobile device for mobile tracking. This device mainly consists out of a GSM mobile phone with a GPS module.
I use this device to send twitter messages with my actual position. This feed can then be used with
twibble to get a track displayed in Google Maps.
The module is programmed in Python. Source and schematics are available.
If that sounds cool, then have a look at tinkerlog:
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Using twitter and twibble for mobile tracking
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DIY mobile tracker