No sure if its the same case (probably is) but I read that he was using those pay-as-you-go phones, and they have a GPS built into them, and since it comes pre-wired, he isn't protected from the warrant laws. All they do is engage the radar that all of those phones have. You can turn your GPS off on your phone and you won't be tracked from what I have come to understand...but with those pay ones you cant...? something like that. You'd probably know more though...
when you disable gps that doesnt stop the carrier from getting the signal unless the phone has some sort of rooting/unlocking/jailbreaking. certain carriers like sprint/verizon, the CDMA no sim chip types are even tougher to completely remain off the grid.