Callers will be automatically translated to that country's particular emergency number. For GSM mobile phones access is provided regardless of the presence or validity of the SIM card within the phone, or whether the keypad is locked.
Warning: '112' is primarily integrated with the GSM network, it may not work if the phone is connected to another type of network such as CDMA. Some mobile carriers have enabled '112' access in their CDMA mobile phones but it is best to check this.
It is certainly useful to know about '112', mobile phone users should be aware that this emergency number may not work in every part of the world or for every mobile network.
‘112’ attempts to connect to any available network, it will not work if no signal at all is available despite rumours to the contrary.
Testing 112 just to see if it works is irresponsible. Emergency call services already have to contend with prank calls without having to take calls from someone testing to see if it really works. Take our word for it - it does! Remember, unless it's hurricane season and you're being whisked off to Oz in serious trouble - don't do it.
Futher Reading:
New Design for 112 Emergency Service
Wikipedia Entry on Emergency Telephone Number
