The 312 area code covers downtown Chicago, Illinois. It covers the Chicago Loop and surrounding areas of the city of Chicago. It is roughly bounded by North Avenue on the north, Ashland Avenue on the west, Lake Michigan, on the east, and 31st Street on the south. By land area, it is one of the smallest area codes in the nation, encompassing only a few square miles.
The rest of the city of Chicago is in area code 773, and the new 872 overlay area code serves the entire city.
That depends on what part of 001 312 is your international dialing prefix. Different countries use different prefixes for outbound international calls, making it confusing to include your prefix.
If your prefix is 00, then you're asking about +1 312, which is Chicago, USA.
If your prefix is 001, then you're asking about +31, which is the Netherlands.
If your prefix is 0013, then you're asking about +1, which is North America, including USA, Canada, and certain Caribbean/nearby islands.
It is much less confusing to quote an international telephone number in correct international format, beginning with the single plus symbol and the proper telephone country code. Note that telephone country codes never begin with zero.
(The plus sign means "insert your international access prefix here." From a GSM mobile phone, you can enter the number in full international format, starting with the plus sign. The most common prefix is 00, but North America (USA, Canada, etc.) uses 011, Japan uses 010, Australia uses 0011, and many other countries use different prefixes.)
North American area code +1 312 is in downtown Chicago, Illinois.
International country code +31 is the Netherlands, and a number beginning with +31 2 is a landline.
+31 is the Netherlands
The country code and area code of Mhlume, Swaziland is 268, 312.
The country code and area code of Ankara, Turkey is 90, (0)312.
The country code and area code of Sawakin, Sudan is 249, (0)312.
The country code and area code of Uzhhorod, Ukraine is 380, (8~0)312.
The country code and area code of Colima- Col., Mexico is 52, (01)312.
The country code and area code of San RamÌ_n, Uruguay is 598, (0)312.
The country code and area code of Gyumri- Shirak province, Armenia is 374, (0)312.
The country code and area code of Baoding- HEB, China is 86, (0)312.
The 312 area code is used for downtown Chicago. It is is unusual in that it is completely surrounds by another area code which is 773 and covers the rest of Chicago.
Area code 312 is downtown Chicago. It includes the Chicago Loop and the immediate area around it. The 312-273 prefix is mostly for wireless users (cell phones), but may also include some landline numbers. Area code 773, which serves the rest of Chicago, completely surrounds area code 312; area code 872 is an overlay on both 312 and 773, serving the entire city of Chicago, but not the suburbs.
US area code 872 is Chicago, IL, overlaying 312 and 773.
St. Charles, Illinois, changed from area code 708 to 630 in 1996.St. Charles was in area code 312 until the 312/708 split in 1989.