I see from Kindle website that there is 3G cover in Kunming.

Is anybody using Kindle's free 3g in Kunming?
What is it like?

It should work. It basically depends on roaming agreements. The US Kindle has an AT&T sim card inside, the UK one has a vodafone sim card inside. Both of these networks have roaming agreements with China Mobile and China Unicom. Therefore if you are near a Unicom 3G signal it will use Unicom, if not it will probably use China Mobile as their EDGE is faster than Unicom's GPRS. You are not charged for roaming - the cost of buying the books is supposed to cover that.