Make sure your service provider can offer China Roaming before you leave home. It's often not included in the "standard" international roaming package.
Kunming, Guilin and other cities in PRC are no problem from coverage point of view.
By the way: the cheapest way to go is if you simply buy a pre-paid SIM card from one of the major networks upon arrival in China - saves you lots of roaming charges.
[ 01 November 2001: Message edited by: Hooking Fell ]