Check out the coverage map:
http://client0.cellmaps.com/tabs.html#cellmaps_intl_tab
tl;dr
There is 3G coverage in LOTS of places. But the best coverage is in the US, followed by Europe. Australia has 3G coverage all along the coasts and, like, places people actually live

but the center of the continent is barren in 3G as well as people.