Under the “wallet” section, there is an option to top up your mobile phone (general add money or buy data only).
They are cheap, easy to recharge credits, and you can get connected in virtually a couple minutes.
Just make sure that your phone is already unlocked, and you will have no trouble using a new SIM.
It covers nearly 90% of the population, so chances are you will be covered wherever you are.
Network: China Telecom uses a CDMA network which is incompatible virtually all phones purchased outside China. It has 3G / HSPA that works with international mobile phones and the coverage is almost as good as the leader, China Mobile.
If you are thinking of purchasing a phone that only works in China (why you would do that, I have no idea), then I guess you could look at China Telecom. China Mobile has a weird 3G CDMA standard that works mostly with phones purchased in China.