Most of the cellphones bought in foreign countries like US, Germany, Japan and South Korea, even the 3G (the third generation) cellphone, can not be normally used in China since different countries in the world have different network service systems. In China, only GSM and CDMA systems are available. Besides, the working frequencies are different for different countries. A frequency of 900/1800Hmz only can be recognized in China. So the best thing is to purchase or rent a cellphone in China itself when you are here for your trip. Many well-known world class brands of cell-phone like Nokia, Motorola, Siemens, Sony Ericsson, Samsung, NEC, Philips, Panasonic, among others, are sold in franchised stores or large-scale emporia of China. After you purchase a new cellphone in China, it will be necessary to have a new Chinese SIM card inserted in the cellphone. Different mobile carriers have different SIM cards. You can shop around and choose the one that suits you.