You can make your phone number come across to any other phone user as a "private" call, by placing #31# in the front of the dialling number.
eg: #31#041-234-5678
As a Telstra mobilenet customer, I have the ability to track other Telstra users, providing they give you permission. At any time I can see a proximity of where my parents or girlfriend are. Only problem is they have the ability to see where I am also! It uses the mobile towers.
