A look at some History:
The ability to dial a single number to report emergencies was first used in Great Britain, in 1937. The British could dial one number to call for police, medical or fire departments, from anywhere in the country.
In 1958, the American Congress first investigated a universal emergency number for the United States and finally passed the legal mandate in 1967.
The new emergency number had to be three numbers that were not in use in the United States or Canada as the first three numbers of any phone number or area code, and the numbers had to be easy to use.
Other considerations were that it should be easy to find on the telephone dial or easily dialed in the dark. The telephone industry decided on the digits "9-1-1".
The very first American 911 call was placed on February 16, 1968 in Haleyville, Alabama made by Alabama Speaker of the House, Rankin Fite and answered by Congressman Tom Bevill.
From then till now:
The Federal Communications Commission (FCC) has taken a several steps to increase public safety by coordinating development of a nationwide, seamless communications system for emergency services that includes the provision of location information for wireless 911 calls. They have taken this approach in phases:
Phase 0 was the initial phase required by the FCC, which mandates that a caller can dial 911 from their cell phone.
Phase 1 mandates that cell phone carriers provide the telephone number of a wireless 911 caller and the location of the antenna (cell site) that received the call. This information is important in case the call is “dropped” and may allow the 911 Call Taker to work with the wireless company to identify the wireless subscriber. The problem with Phase I is that it does not allow Call Takers to locate emergency victims or callers.
Phase 2 mandates that carriers provide far more precise location information – within 170 to 1000 feet. The various carriers have developed different methods to provide the latitude and longitude from the cell phone handset. It can be from triangulation, GPS or a hybrid of the two.