- Stream your phone's video feed live to the world. (Could also be used by jealous husbands and wives, and when I think about it, the porn industry could be a major driver of this feature.)
- Extreme live blogging/twittering: I don't think how much more live and extreme this kind of blogging can be? If you would have a temperature sensor (and I don't see why you couldn't), your blog could adapt on the fly to the weather circumstances :-)
- Dating: when you enter a room or club, some wicked Personal Area Network detects all the participants and feel free to browse the profile pages from everyone around you.
- IPv6: if all those millions of phones start hitting the internet, I think we'll run into troubles with the amount of available IPv4 addresses, so we need to switch to IPv6
- Performance: when you're John Doe that wants to show off his cats to the occasional visitor, no problem. If you are some kind of porn star or just... popular, what if hundreds of people start hitting your mobile site? Can't imagine that your phone can handle that.
- Security and privacy: well I don't think I really need to explain you what kind of security and privacy nightmares this can cause?
- Bandwidth and costs: will UMTS be enough? And how much money will these huge data transfers will cost you (in case you want to live stream your video feed ;-) )