USUALLY each city has its own area code,but when I called one of my classmates in the U.S.the display on his telephone showed codes for three cit ies(Changsha,Xiangtan and Zhuzhou)He was puzzled and asked me whether I had opened companies in all three cities.I told him that as a city group the three cities use a unified area code–one of the results of regional econom ic integration.My company is in Chang USUALLY each city has its own area code, but when I called one of my classmates in the US the display on his telephone showed codes for three cities (Changsha, Xiangtan and Zhuzhou) He was puzzled and asked me whether I had I opened a deleted company in all three cities.I told him that as a city group the three cities use a unified area code-one of the results of regional econom ic integration .My company is in Chang