Hey guys, let's put our heads together and put a definitive source for all the best GSM service providers worldwide. So that when we travel to a foreign country, we know which provider's sim to buy.

United States
T-Mobile

Post Paid Sim: low voice rates, gprs data, need to apply for credit
Pre Paid Sim: Tmobile, high rates, no gprs, no application needed

China
China Mobile

GoTone: must apply with passport, best rates for voice because you have monthly packages, but you must pay every month, international roaming, gprs, voicemail, lots of services, can pay you bill by buying little recharge cards anywhere in China, need mailing address in china so they can send you bill if you go over your balance, convertible to Mzone. good for if you want to able to receive calls/sms when out of china

MZone: don't need passport, no voice plans, and no monthly bill, 300 free sms messages, if you use up your money, will not extend you credit, no international roaming, can only buy recharge cards in the province you bought it in, but can recharge nationwide in large banks, good for if you have no permanent business in china and just want to be able to call people locally, has gprs, voicemails, same as Gotone, except no included minutes and no international roaming, convertible to Gotone

Shenzouxing: can charge nationwide with recharge cards, national roaming, no international roaming, not covertible to gotone or mzone, no gprs, no voicemail, no extra services, just plain phone, not recommended.