I came across these handy tips for China Mobile users in a magazine recently (thanks That's Shanghai!) and wanted to share:

To check remaining credit, text YECX to 10086.

To check used credit in the last month, text 102 to 10086.

For international long distance calls, call 10086 and ask them to activate your international service.

After this is done, dialling 17951 before the international number gets you a discount on the long-distance charges.

17951 also reduces the cost for calls made outside your local calling area (these can really eat into your credit without realizing it and leave you incredibly irritated in say Hangzhou with a Shanghai SIM, and unable to buy top up vouchers.)

Calling 1860 gets you roaming services in Hong Kong, Macau and Taiwan (call before leaving the mainland)

Call 10086 from mainland China to get other international roaming services activated - if you are already outside of China, call +86 1380 010 0186.

Text kt20 to 10086 for roaming internet services.

And perhaps most important of all... to change the music that everyone hears when they call your phone, (set all too often to wailing Chinese love songs of bad elevator music), call 12530. Or choose a song at www.music.10086.cn and text the name to 1065 8830 to download it staright to your mobile.

As a side note, if you lose your China Mobile SIM, you can call 10086 to cancel your current SIM card and go to a China Mobile store to get a replacement one withthe same number. Proof of purchase/ownership may be required in the form of the original SIM card package or you can tell them 10 numbers you have called in the last three months and they'll check the records to confirm it's you.

If anyone has any other useful tips along these lines (maybe for China Unicom??), please wing them this way!