Suppose I have access to the cellphone in question. I want to put a tracker of some kind, so that I can see the location of the phone at all times, preferably with my own phone. The owner cannot know. What kind of software and costs am I looking at here?

=CK=

cell phone gps is not gps as far as i know.

I think it has to do with triangulation. the phone gets a signal from 3 or more towers, and using some simple math, it figures out where you are.

The only way you could get it on a cell phone would be throught the service provider. (Verizon, Sprint etc.)

So if you control the account, then yes.

If not, no.