Using actual GPS on cell phones is not practical. I own a GPS (Garmin Etrex Venture) and I use it a lot -

1. its big and bulky, by itsself it dwarfs my korean cell phone. Do you want to see a REAL GPS phone? try this, Its a brick!
2. in Seoul, large building are always blocking the satellite signal making it damn near useless
3. in the woods/mountains, it requires my constant attention to get a fix
4. on a bus/plane etc I usually have to wave it around for a few minutes until I find a "sweet spot" where I can find a signal and get three satellites.
5. Man it sucks up batteries!American cell phones have crappy battery life as it is, you would be lucky for yor cell phone to last 6 hours!
6. They take at least 30 seconds to initialize/communicate with the satellite so that you can get a fix with them.

If you really want to track someone with GPS goodluck. E911 is different, it uses cell phone towers to triangulate your position. Those signals, unlike those from GPS satelite can't be blocked by tinfoil.

Sleep well!

Regards,
Justin