"home zone" functionality
openmoko at kironet.de
Thu Apr 17 11:48:09 CEST 2008
this is my first post to this list, but I read it for over a year now ;-)
If i remember correctly, on the SIM-Card is an center and an radius
defined and stored. These values are renewable via SMS, but this is only
done by the network operator when you change your "Homezone" to another
In germany in the o2-network every antenna sends its own coordinates in
form of a 12 digit number called "Gauss Krüger Koordinaten"   on cell
broadcast channel 221. The SIM calculates, if it is inside the circle
which is defined by center and radius and displays via the SIM-toolkit a
picture (house) on the display of the phone.
If you want to know more about this, you should look at nobbi.com where
I found this information years ago. He has developed a Software called
SIMspy2  (windows binary only), which can read these stored
coordinates, but there are sources too for an older version of it .
And for the hackers of you, AFAIK you can change the coordinates in your
SIM by sending a special SMS to your phone, but this changes only the
coordinates on your phone. The real billing is done via the network
operator and is indepndent from what your phone thinks he is "at
To see how such a homezone works, have a look at my homezone .
Note the values center(X,Y) and radius on the page.
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