Sounds like your phone is backward compatible to GSM as China Mobile's legacy network is GSM with the data supporting GPRS/EDGE, which means you can NOT use China Mobile's 3G-TD-SCDMA network with your mobile phone (and some pundits say data still sucks using China Mobile's alleged 3G phones). The solution is a TWO-STEP process as follows.
STEP 1 - THE APN & 3G SETTINGS
The APN is: cmnet
Upper/lower case - doesn't matter.
Don't need anything else as far as software settings go, EXCEPT you'll probably need to manually turn OFF or disable the 3G mode on your mobile, if such a thing is possible - should be a software setting somewhere.
STEP 2 - ACTIVATING THE BILLING
If you haven't activated data on your China Mobile BILLING plan...go to an official store WITH YOUR ID (e.g. passport) and pay/pre-pay the data plan fee. I think you can still get 2GB of EDGE data for ¥100. You MAY be able to do this via the appropriate SMS to the China Mobile service center - but I've never found this painless process for Kunming - so off to one of the myriad China Mobile stores you go.
EDGE is typically only available in the inner city and the older high density suburbs. The speed difference on similarly loaded networks should be about 10:1 on a good day - depends on a multitude of things and I'm too lazy to give a technical dissertation on 3G.
If all this sounds painful...well, it is.
I switched to WCDMA/Unicom recently as have most of my data hogging peers - but that probably has something to do with the iPhone 4 promo. Data coverage is not so bad and getting better. The speed is snappy compared to China Mobile's EDGE network, which looks really crappy compared to 3G.
One note - China Mobile merged with China Railroad (Tietong) Telecom - which had a 2% market share in the broadband market - which basically means their broadband pipe is ... asthmatic. So, even if you have great signal - during prime time their internet pipe is a bottleneck.
China Unicom M&A'd with China Netcom (major competitor to China Telecom) - which was the #1 or 2 (depending on where you are in China) provider of broadband and fixed line services. Their internet pipe is BIG - comparable to China Telecoms.
Like I said - it's complicated - that and all the providers lie (a lot) about various things as they're all trying to delay heavy 3G infrastructure investment in favor of LTE, which according to NTT (Japan) can now achieve GIGABIT download speeds, so they're all fixing the various weaknesses in their infrastructure. China Mobile's buying more broadband pipe, Unicom is looking for more cell sites, and Telecom hates that they got stuck with CDMA (US standard) - they're also trying to densify their cell sites.