Heiko Hebig has some good real-world observations about mobile Internet access:
"There you have a crowd of 150 well-equipped gadget freaks and Internet addicts in Western Europe and none of them even considers to convert to [mobile phone-based] data-traffic for as long as the next WLAN hotspot is not too far away and their lives don’t depend on connectivity. Why is that? Is it because one hour of data traffic via your network still costs more than the air fare to Vienna? Is that because I don’t even know how much one hour would cost me when I dial-up from a different network or (even worse) another country?"