Can I use my iphone in china?

I'm a US citizen I will be studying in Beijing over the summer for 6 weeks.
Will I be able to bring/use my iphone 4s?
Can I make calls to the US?
Can I text to the US?
Can I use it for Gmail or yahoo mail?
Can I browse the internet on it?

Yes to all - but if using your US SIM, roaming, the charges are really high

Alternatively, you can:

- use your Wi-Fi and run Skype with SkypeOut account on your iphone
- get a Chinese SIM for your iphone or get a cheap local phone (you can get an unlocked nokia for $50) and use it for calls
- do the above and get a SkypeToGo number

You can also try funny chinese phones like myPhone, iFone etc.