Police in this country routinely use pinging when they get court orders for cell-site locator information. They call the phone and "ping it" to see what cell tower it's near. That lets them know where to send physical surveillance officers. If the suspect is at home, there's a big Fourth Amendment issue and many magistrate judges around the country have denied pen register requests that include cell site locator information for that reason: a pen register can be gotten with a court order that the information sought is relevant to an ongoing investigation, while a search warrant establishing probable cause should be required to "ping" someone in their own home.
The Third Circuit, the first appeals court to consider whether a search warrant is necessary for cell site locator information ruled the warrant is optional. More here.
Disclosure of cell site information turns a mobile telephone into a "tracking device" and disclosure should not be authorized without a showing of probable cause.
Cell site data provides the location of the cell phone tower supplying service to a cell phone during a telephone call. It can be obtained from the cell phone service provider within a few seconds of the call.
Geo-location information provides the location of a cell phone within several hundred meters. In providing the information to the Government, cell phone companies are informing it of the specific location of a phone at a particular time.
In some cases, the Government asks for cell site location data not just of the phone it is investigating, but for all numbers dialed to and from the phone. That could be anyone.
Also see, EFF here.
'Pinging' is a big deal, and is used widely by law enforcement here. Congress should make it clear that pinging requires probable cause and a warrant, just like a wiretap order or a search warrant.