I, like Anxiao, have used China phones for years in the US. Here is the catch -
1. You need to buy the right GSM phone in China to support US freq. 850/1900
2. Prepare to pay US 300 to 500 in China for a good 正行货 mobile phone (RMS 2500 to 4000). 水货,假行货 are every where in the china market place, bring an local Chinese who in the knows to shop for you
3. If you are in HK or Singapore, you get the same phone in China for about 70% of the China price.