MADISON, Wis. -- As questions remain about what might have transpired over a 911 call from Brittany Zimmermann's cell phone sometime before she was killed last month, local dispatchers discussed ever-changing protocol as 911 calls are increasingly made on cell phones.

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Dispatchers at one of the state's most advanced emergency call centers in Rock County said that more than 60 percent of the area's 911 calls are made on cell phones.

And as call centers continue to adapt to the growth in mobile technology, dispatchers said there is more and more protocol to juggle, all while handling an infinite number of emergency scenarios.

The first question 911 dispatchers ask is: "Where is your emergency?" But when it comes to cell phones, dispatchers said that is often the hardest question to answer.

"Cellular phones are a radio communication device, and as such, radio waves are not landlines, where you can count on them to work all the time," said Dave Sleeter, 911 communications director in Rock County.

According to area dispatchers, emergency calls made on cell phones fall under three "phases," which were developed by the Federal Communications Commission.

In Phase Zero, the dispatcher receives only the caller's phone number. In Phase 1, the dispatcher can identify the specific cell phone tower from where the call is coming. In Phase 2, dispatchers are usually able to locate the caller's phone using Global Positioning System technology within 300 meters.

Even with Phase 2 calls, dispatchers said that hang-ups are difficult to pinpoint.

"As we get Phase 2 GPS 911 calls that are abandoned, we put the latitude and longitude in, and it plots it on the map. We look at the closest intersection, the closest structure, and then identify it from the map, where that closest structure could be," said Shelley Schmidt, dispatch shift supervisor at 911 Communications in Rock County.

Regardless of how little information they gather, Rock County's 911 dispatchers said they're required to respond to every call in some way.

"We've always, always sent. Someone needs the service; we send the service. We just do a little bit more confirming or a little more digging of the caller. If they don't know where they are, it becomes more of a question and answer," Schmidt said.

But dispatchers said that cell phones can leave more questions than answers.

"It's very new technology. It has brought a lot of advantages for people that are mobile and through society as a whole. But as with any technology, there are limitations," Sleeter said.

The Rock County 911 call center said that when it comes to under which phase a cell phone call might fall, a number of variables come into play, such as the lay of the land where the call is being made, the weather, the cell phone provider and even the timing in which the call is answered.

Dispatchers seeking more information from a cell phone call can attempt to get a stronger signal through a tracking process called "rebidding," which works only if the phone contains a GPS chip. Cell phone providers were required to include GPS chips a few years ago.

GPS Systems On Cell Phones Helped Friends In Quarry

GPS systems on cell phones are helping save lives in the area, including five friends in a Middleton quarry in July 2007.

Six friends, all in their early 20s, were shooting off fireworks in the quarry, and when they tried to leave, they lost their way. The truck plummeted 70 feet, landing on its roof.

One of the passengers used his cell phone to call 911.

"They said they were at the quarry outside of Middleton. I got them on GPS -- Middleton, Highway 12 north of Parmenter," said a 911 dispatcher.

"The concern was, we have more than one quarry in our area. The GPS technology was able to locate them at the Parmenter Street quarry, was able to dispatch the units to that location and quite possibly save their lives," said Aaron Harris, chief of the Middleton Fire Department.

Harris said that in the quarry incident, time was a major factor. One person was killed, and four of the five others were hospitalized.

Because there was some information before the caller's cell phone died, rescuers were able to determine at which quarry that incident occurred. If they had to search for the victims, it might have been a different outcome.