I travelled to Beijing and Xian a few months ago, I suppose that the situation in Canton is similar.

China uses GSM, so your phone should support that (and not CDMA, which I think that alltell is using). Data service via GPRS should work, although I did not try it. No UMTS coverage as far as I know. It is also very expensive, so you are most likely to use wifi anyway.

Wifi or an ethernet port in your room should be available in all hotels catering for westerners. Personally, I always carry a small wifi router with me on travel to use the ethernet port when available. Connection speed is good, gizmo worked but the quality was low (but gizmo's quality has always been low on the phone numbers I call which are in Europe).

You might find open wifi access in some western style cafes or malls, but it is not common.

China blocs Internet access to some sites, most notably the BBC. Direct connection to the i.p. address should work however. If there is a site that you absolutly need to contact during your trip, I suggest to check its i.p. number from home and take it with you. Do that for your mail server, for example.

PC with Internet access are to be found everywhere, in hotels, in airports and of course in numerous Internet cafes. A web access for your mail may prove convenient. There is a catch however: since I am back I receive about 50-100 spam messages in Chinese. I suppose that a key logger was running on one of those PCs and sniffed my e-mail address. You may want to set up a throw away address for the trip. In any case: change all passwords when you are back and be careful with sensitive information.

Dos:
smile, tell everyone that you find China great, try restaurants who do not have an English menu. Take a book with translations of common terms and food terms in chinese script with you, you can just point at what you need this way. Take maemo mapper with satellite images of the city with you, it helps to understand in which part of the city you are. I did not find any maps of China online down to street level, so satellite was the only choice. You'll find tourist maps on the spot (and they are good, with Chinese script and English translation), but finding the name of the street you are in can prove difficult. Ask your hotel for their card (with directions in Chinese script) so that you can show that to any taxi and be brought back home. If you are not picked up at the airport, it also helps to get the name and address of your hotel IN CHINESE SCRIPT before you leave: most people can't read our script in China.

Don't:
criticise, lose your temper. Don't use taxis offered in the airport hall, go to queue at the taxi stand with the Chinese (you'll jump the queue anyway). Don't try Szechuan cuisine if you do not like your food unbearably spicy. Don't try to order fancy foodstuff (snake, dog, etc...) unless you want to treat Chinese people (Chinese doing business seem to believe that the more important the contract, the more expensive the food must be).