I don't think iphonebrowser works for the 3g currently, but I'm not sure. I know you at least need an jailbroken iphone, if you want to get outside of the "sandbox" that is. BTW I really enjoy using this program as it is an excellent utility for accessing your iPhone filesystem from windows.
Iphonebrowser:
Download:
iphonebrowser - Google Code
MMi disscussion
iPhoneBrowser 1.50