I did not know that yesterday!

We've all seen movies where the cops try to dupe some telephoning wacko into droning on about his plans to blow up Rhode Island, just long enough to complete a trace on the call. But Slate's Explainer describes how this longtime Hollywood trope no longer applies:

"Tracing problems are a relic of manual switchboards, which required operators to physically connect circuits. In order to track down a caller's location, police needed 10-20 minutes to figure out the maze of circuits....shorter calls could only be traced back...to a nearby switching station rather than the source phone."

But phone companies started using electronic switching systems in the mid-1980s, so that a caller's number could be identified almost instantaneously, and cross-checked with an "automatic location indicator" for the address. Furthermore, many systems now include a call-tracing feature, triggering a trace when customers dial *57.

The originating location of many cell phone calls, however, remains untraceable. (In 2003, only 15 percent of 911 centers could trace cell phone calls.) This inability has presented a problem for emergency service personnel, sometimes leading to tragedy. Although the FCC set a deadline of December 31, 2005 for "enhanced 911 services," in which carriers should have equipped 95 percent of subscribers with "location-capable handsets," the phone companies are behind schedule. More and more counties, however, are instituting cell phone tracing. And while privacy advocates may not be thrilled, those guys from "The Wire" should be happy.

Source : ask.yahoo.com