i found one plugin http://wordpress.org/extend/plugins/ochre-w3c-geolocation-services, close to my demand but it seems still need revise some code on the activated theme.
so i am wondering, if any easy to use plugin with such feature:
for example, provide a widget or shortcode with a button, whenever visitors come from a mobile browser and press that button, he will get his accurate location and content info related to that location, which is predefined and inputed by site admin.
if there is no such plugin yet...i think it's a good blank. anyone build it will get lots of wp users i believe,that is a basic and common demand in turning wordpress into mobile era.
btw...i am not a programmer.