If time permits, you might want to try to grab a SIM/plan on eBay. Also, for long term visitors, there are some sick tuangou deals out there (e.g. y1500 for 2 years with 700 mins of talk time per month and more than enough data for most people). Telphony/internet is one area in which China is much cheaper than most other countries. I even use my China numbers when I'm in the US/Europe because roaming rates aren't really any higher than prepaid SIMs.