Emergency telephone number
Many countries' public telephone networks have a single emergency telephone number, sometimes known as the universal emergency telephone number or occasionally the emergency services number, that allows a caller to contact local emergency services for assistance.  The emergency telephone number may differ from country to country.  It is typically a three-digit number so that it can be easily remembered and dialed quickly.  Some countries have a different emergency number for each of the different emergency services; these often differ only by the last digit.

# Use of emergency numbers
In most areas, the emergency number is intended to be used only in an emergency. Routine and non-urgent calls as well as hoax or prank calls to emergency services numbers waste the time of both dispatchers and emergency responders and can endanger lives.  False reports of emergencies are often prosecuted as crimes.
For routine and non-urgent enquiries emergency services generally provide traditional telephone numbers for contact.  These are normally listed in the local telephone directory. In England and in Wales, for example, where serious emergencies have a three-digit number 999, the number 0845 46 47 can be dialled for NHS Direct, a non-emergency medical service. (In Scotland the number 08454 24 24 24 is used to connect to NHS24, the equivalent service).
In many areas in the North American Numbering Plan, 311 has been assigned as an urgent telephone number that may be used to contact the police and other services to report minor incidents and historic crime that does not endanger life, to avoid overloading 911.  Other cities in North America use 311 as a general contact number for municipal government or for reporting situations such as power outages.
The telephone number 112 is the international emergency telephone number for GSM mobile phone networks. It does not necessarily work on mobile phone networks based on other technologies. In all European Union countries it is also the emergency telephone number for both mobile and fixed-line telephones.
To avoid overloading the European normal 112 number, Sweden has an automatic routing of the incoming phone calls. If the local emergency center is overloaded the call will be routed to an another emergency center that's not overloaded, thus avoiding queuing of emergency calls.

# Emergency numbers and mobile telephones
The GSM mobile phone standard includes 112 as an emergency number, and in countries where 112 is not the standard emergency telephone number, GSM telephone users who make calls to 112 generally have their calls redirected to the local emergency telephone number, if it exists. This is valuable for foreign travelers, who may not know the local emergency number.  Most GSM mobile phones can dial 112 calls even when the phone keyboard is locked, the phone is without a SIM card, or instead of the PIN.
Using 112 instead of another emergency number on a GSM phone may be advantageous, since 112 is recognized by all GSM phones as an emergency number.  A phone dialing a different emergency service's number may refuse to roam onto another network, leading to trouble if there is no access to the home network.  Dialing 112 forces the phone to make the call on any network possible.  However, some GSM networks (e.g. in Belgium, Spain, UK, Liechtenstein, Austria) are reported to connect emergency calls only from phones with a valid account on their network, e.g. customers and roamers only. Some GSM networks will not accept emergency calls from phones without a SIM card, or even require a SIM card that has credit. Latin American GSM networks typically do not allow 112 calls without a SIM.
Not all countries treat wireless emergency calls in the same way. In general, a country's emergency numbers will all route to 112 as a single point of contact for mobile-originated emergency calls. By contrast, Singapore treats 995 calls for Fire or Ambulance as an emergency call but these calls are not routed to 112. So the phone will dial this number using emergency rules but the call routes to 995 not 112. In Singapore, 112 is only for the Police.
In the United States, the FCC requires networks to route every mobile-phone 911 call to an emergency service call center, including phones that have never had service, or whose service has lapsed.  As a result, there are programs that provide donated used mobile phones to victims of domestic violence and others especially likely to need emergency services.
Mobile phones generate additional problems for emergency operators, as many phones will allow emergency numbers to be dialed even while the keypad is locked.  Since mobile phones are typically carried in pockets and small bags, the keys can easily be depressed accidentally, leading to unintended calls.  A system has been developed in the UK which connects calls where the caller is silent to an automated system, leaving more operators free to handle genuine emergency calls.

# Configuration and operation
The emergency telephone number is a special case in the country's telephone number plan.  In the past, calls to the emergency telephone number were often routed over special dedicated circuits.  Though with the advent of electronic exchanges these calls are now often mixed with ordinary telephone traffic, they still may be able to access circuits that other traffic cannot. Often the system is set up so that once a call is made to an emergency telephone number, it must be answered. Should the caller abandon the call, the line may still be held until the emergency service answers and releases the call.
An emergency telephone number call may be answered by either a telephone operator or an emergency service dispatcher.  The nature of the emergency (police, fire, medical) is then determined.  If the call has been answered by a telephone operator, they then connect the call to the appropriate emergency service, who then dispatches the appropriate help.  In the case of multiple services being needed on a call, the most urgent need must be determined, with other services being called in as needed.
Emergency dispatchers are trained to control the call in order to provide help in an appropriate manner.  The emergency dispatcher may find it necessary to give urgent advice in life-threatening situations.  Some dispatchers have special training in telling people how to perform first aid or CPR.
In many parts of the world, an emergency service can identify the telephone number that a call has been placed from.  This is normally done using the system that the telephone company uses to bill calls, making the number visible even for users who have unlisted numbers or who block caller ID.  For an individual fixed landline telephone, the caller's number can often be associated with the caller's address and therefore their location.  However, with mobile phones and business telephones, the address may be a mailing address rather than the caller's location. The latest "enhanced" systems, such as Enhanced 911, are able to provide the physical location of mobile telephones.  This is often specifically mandated in a country's legislation.

# History of emergency services numbers
When an emergency happened in the pre-dial (or "manual") telephone era, the user simply picked up the telephone receiver and waited for the operator to answer "number, please?"  The user responded with "get me the police," "get me the fire service," or "I need an ambulance/doctor."  Even in a large city it was seldom necessary to ask for these services by number.
In small towns, operators frequently went the extra mile by knowing where to reach doctors, vets, and law enforcement personnel at all times.  Frequently, the operator was also responsible for activating the town's fire alarm.
When manual switching systems began to be replaced by automatic, or "dial" systems, there was frequently concern among users that the very personalized emergency service provided by manual operators would be lost.
This problem was at least partially solved in the USA, Canada, and the UK by dialing "0" for the local assistance operator in case of emergency, although faster service could be obtained if the user dialed the full number for the Police or Fire Department.  This system remained essentially unchanged throughout most of North America until the 1970s.
The first emergency number system to be deployed was in London on June 30, 1937. When 999 was dialed, a buzzer sounded and a red light flashed in the exchange to attract an operator's attention. It was gradually extended to cover the entire country, but it was not until the late 1970s that the facility was available from every telephone.
In the days of loop disconnect dialing, attention was devoted to making the numbers difficult to dial accidentally by making them involve long sequences of pulses, such as with the UK 999 emergency number. This contrasts to modern times, where repeated sequences of numbers are easily dialed on mobile phones, particularly as mobile phones will dial an emergency number while the keypad is locked or even without a SIM card. Some people in the UK have reported accidentally dialing 112 by loop-disconnect while working on extension telephone wiring, and point to this as a disadvantage of that number.
The first North American emergency number was the 999 system deployed in Winnipeg, Manitoba, Canada in 1959 at the urging of Stephen Juba, mayor of Winnipeg at the time. The first US 911 emergency phone system was set up in Alabama in 1968, but it was not in use everywhere until the 1980s to standardize the number across most of the NANP, Canada switched to using 911 as its emergency number in 1972. (Some Caribbean islands use 999.)
The implementation of 911 service in the USA was a gradual and haphazard process.  The chief obstacle was the fact that telephone service boundaries seldom, if ever coincide exactly with governmental and other jurisdictional boundaries.  In other words, a user might dial 911, only to discover that he had been connected to the wrong dispatch center because he had telephone service from one location, but lived within the boundaries of another jurisdiction.
Furthermore, a great deal of electromechanical switching equipment was still in use, and much of it was difficult if not impossible to adapt to recognize 911, especially in small towns and rural areas where the call might have to be switched over a considerable distance.  For this reason, it is still not unusual for a County Sheriff's Department to have an "800" (long distance, toll-free) number.
Gradually, various problems were overcome; "smart" or "enhanced" 911 systems were developed that not only displayed the caller's number and address at the dispatch center, but also could be configured so that 911 calls were automatically routed to the correct dispatch center, regardless of which central office the caller was served from.
The rapid replacement of electromechanical switching systems in the 1980s with electronic or digital systems eliminated the problem of older switches that would not recognize 911.  At this point, 911 service is available in most of North America, but there is still the occasional small, remote town that does not have it.
In France, in 1928, telephone operators had to connect the calls for emergency reasons even when the phone service was closed.  In 1929, an automatic connection system was set up, initially for fewer than 10,000 people in Paris, allowing them to dial 18 to reach the fire brigade.  The service was not widespread until the 1970s.
The CEPT recommended the use of 112 in 1972.  The European Union subsequently adopted the 112 number as a standard on 29 July, 1991.  It is now a valid emergency number throughout EU countries and in many other CEPT countries.  It sometimes works in parallel with other emergency numbers in countries such as Britain and Ireland.

# Emergency numbers

## Worldwide 767
Subscribers of Iridium Satellite phone and SOS International can dial 767 (SOS) to get help or medical evacuation to the nearest SOS International medical centre.
This number has not been yet installed in fixed telephony.

## Africa

## Asia

## Europe
The most common European emergency number 112 (following Directive 2002/22/EC - Universal Service Directive) and also standard on GSM mobile phones. 112 is used in Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Liechtenstein, Lithuania, Luxembourg, Republic of Macedonia, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, and the United Kingdom in addition to their other emergency numbers.(sources: European Radiocommunications Office, European Union, SOS 112 Europe, latest status on E-112 initiative:  /).

## Oceania

## North America

## Central America and the Caribbean

## South America