Illinois is the state that has 312 as an area code on cell phones. This has been the existing area code since 1947. It covers three counties, 528 ZIP codes, and 364 prefixes. Check out all these prefixes and the counties they represent at phones.whitepages.com.
North American Area code 312 is the area code for downtown Chicago, which includes the Chicago Loop and its immediate environs. It is completely surrounded by area code 773, which serves the rest of Chicago. source: wikipedia http://gg.gg/publicrecords can help you for similar problems tnx