Track and trace SIMs...without consent!

It was brought under my attenti0n that there exists a method to retrieve geographical information on a SIM by knowing only the subscriber's phone number. Phone-hunter is a service that allows you to do just that. Enter the phone number of the subscriber you would like to track and the website returns the area where the SIM was last registered. This area corresponds to an area of a switching center. The details of the method are described here and I will provide a short summary:

Telecom providers need to know where their subscribers are located. To this end, they keep a record of which subscriber is currently located at which MSC. This record is actually queried whenever you send a text message to see where the receiver is at.
To illustrate, when I were to send a text message, the database is queried using the receiver's MSISDN and the query would return the following information:

• The MSC number the subscriber is currently using
  
• The subscriber's IMSI
• Possibly a user error (e.g. "absent subscriber == 'phone is offline')

The database is public for any company that is a 'telecom provider' (which could be in fact any company). A service like phone-hunter will allow you to query this subscriber database given any MSISDN.

Now, the MSC number is unique for each telecom provider and each MSC is bound to a certain geographical region. Given this info it is possible to determine someone's geographical location up to the region of a certain MSC: wicked!
One small challenge is that the mapping from MSC number to geographical location is not readily available, so this is for a lot of area's to be determined.

I can think of a couple applications where this may be interesting (never mind the ethics :)) : tracking employees, tracking wife's, private investigator's doing remote observations, etc.