iPhone users are speculating that the ability to "tether" their phones to their laptops to share the iPhone data connection may be coming in June as part of an iPhone software update. This would be a boon when traveling, as it is tough to do much work that involves writing on the iPhone (or any phone) itself. Even with the now widespread availability of free/fee WiFi hotspots, there are still lots of times when having a data connection on the laptop would be very useful.
Right now, AT&T users can buy one of those little USB wireless modems for laptop connectivity via the cellular network, but it requires a second $30/month data plan. I'd pay extra for iPhone tethering support, but another $30/month is not worth it for how much I would typically use it in a month. I just don't need to be connected all the time, and if I have to wait an hour, it's usually not a big deal.
There have been two things that have probably been holding back the release of this feature. First, the AT&T 3G network has had limited capacity; adding a bunch of people with laptops connected for long periods of time would only make things worse. AT&T has been adding capacity, and if tethering is released, it must mean that AT&T is more confident that its 3G network can handle the load. Second, having your iPhone act as a wireless modem will eat up phone battery life, although you can charge your phone from your laptop. In any case, if this is released, it will make the iPhone even more useful than it already is.