Dial 123 for voice mail.
Dial 450 for top-up service.
Dial 451 for customer service (may or may not be free!).
Dial 452 for rates (may or may not be free!).
Dial 453 to check on credit.

The competitors are BTCellnet (GSM900/GSM1800), One2One (GSM1800), and Vodafone (GSM900/GSM1800). Orange has the best prices for calling US. Orange coverage was pretty good. I rarely went below 4 out of 5 bars.

Dial 222 for call credit via SMS.
Dial 224 to charge up the card.

The competitors are SFR (GSM900) and Bouygues Telecom (GSM1800). Orange had the best rates and one of the two competitors doesn't even offer pay-as-you-go. Coverage was good, average 3-4 out of 5 bars.

To get a cell phone in Italy, you have to provide what is called a Codice Fiscale (a fiscal code), similar to the SSN that we have here in the US. Everyone has a CF, since it is based on where you are born, your birthdate, sex, and name. Goto http://www.comuni.it/servizi/codfisc to get one. Use "Stati Uniti" for United States (the field marked "Comune di nascita"). I used my state for the "Prov." field.

I bought my card for L100.000 at the Roma Termini station downstairs at an electronics store called Giotto. The person there took a photocopy of my passport and my CF number that I had generated. The card comes with L50.000 credit and is charged by the second. The card can roam anywhere in the world, almost. It's parent company is Vodafone. I had problems roaming though, it would not let me call anywhere but back to Italy. I think you can unblock the card by calling customer service, but I didn't really need to, since we were leaving Europe and I didn't want to try to find an English speaking customer service rep. Calls were very cheap.

Patience. I bought the card and was told that the card would take 24 hours to activate. My phone kept reading "SIM Error" or "SOS Calls Only". I got kind of worried and went back twice to pester the store where I bought it. The guy finally told me to go away (literally, but I think he did not know how to tell me to wait longer) and wait and if it didn't work in the morning, then come back. Sure enough, about 5 hours later, it started working. It took about 10 hours to get service started.

The coverage was not as good as in France or UK, but a neat feature is that the phone would tell you what city you were in. Very nice when we were on the train. It's L7 per second to call within Italy, L3.5 per second to call another Omnitel user, and L12 per second to call the U.S. There appeared to be some sort of call setup fee, but I could never figure it out. L200 to send a SMS.

Dial 190 for customer service.
Dial 404 for a SMS with credit remaining.
Dial 414 for a recording (in Italian) of credit remaining in Euro.

Competitors in Italy are Blu (GSM1800), Telecom Italia Mobile (TIM) (GSM900/GSM1800), and Wind Telecomunicazioni (Wind) (GSM900/GSM1800). They all seem to have similar deals as Omnitel, but the people who worked at my hotel said that Omnitel had the best coverage, if this is true, Italian cell phone coverage is just poor. Average was 2-3 out of 5 bars. In the hotel room, I couldn't get a signal half the time.

They speak English or French.

Dial *46 for everything.

Fido (Microcell) is the only GSM provider.

You'll need a GSM900/1800 phone to get coverage in China. I bought the card in Beijing and was able to use it in most of the places I went to in China, including Shanghai. (although, I had a ton of problems getting it to maintain registration in Shanghai, that could have been due to network roaming problems or old SIM, because the exact same card bought in Shanghai worked flawlessly). I had 5/5 bars 90% of the time. Even in the subways of Shanghai and the Mountains of the Great Wall.

The number to dial for service is 13800138000. It is both in Mandarin and English. The instructions are also in (Simplified) Chinese and English.

Dial Internationally by using the + followed by country code. Quality is excellent.

You can buy charge-up cards almost anywhere in 50, 100, 150, and 200RMB increments.

Non Roaming Tariff:
Local calls are 0.60RMB/minute, Domestic Long Distance are 0.60RMB/first minute+0.07RMB/6 seconds. International Calls are 0.60RMB/first minute+0.80RMB/6 seconds. Calls to HK, Macau, and Taiwan are 0.60RMB/first minute+0.20RMB/6 seconds. Receiving calls is 0.60RMB/minute.

Roaming Tarrif:
Local calls are 0.80RMB/minute, Domestic Long Distance are 0.80RMB/first minute+0.07RMB/6 seconds. International Calls are 0.80RMB/first minute+0.80RMB/6 seconds. Calls to HK, Macau, and Taiwan are 0.80RMB/first minute+0.20RMB/6 seconds. Receiving calls is 0.80RMB/minute+0.07RMB/6 seconds.

You can also get China Unicom, which may be better for calling internationally, because I hear you can use an IP Card (front, back) with it to reduce your long distance rates down to 2.4RMB/min.