112 is reacheable even you don't have a SIM inside. The only case I believe it doesn't work is if you are in a country where there is no network your phone can connect to, I thought I saw that when I am in Korea where they use 2100Mhz which my phone doesn't talk to at all.

Here is more info about this number
112 (emergency telephone number)
From Wikipedia, the free encyclopedia

112 is the common emergency telephone number that can be dialed free of charge from any telephone or any mobile phone in order to reach emergency services (Ambulances, Fire & Rescue Service and the Police) in the European Union (EU), its candidates for accession, members of the EEA agreement, as well as several other countries in the world.

112 is managed and financed in the European Union by each Member State (country) which also decide on the organisation of the emergency call centres. The International Telecommunications Union recommends that member states that are selecting a primary or secondary emergency number choose either 911, 112 or both. [1]. 112 is one of two numbers (the other being the region's own emergency number) that can be dialed on most GSM phones even if the phone is locked.[2] The GSM mobile phone standard designates 112 as an emergency number, so it will work on GSM phones even in North America where GSM systems redirect emergency calls to 911, or Australia where emergency calls are redirected to 000