IMPORTANT: New info for jailbreaking

Some changes I have to the stuff that I wrote previously:

1. Install Cydia first. This is a package manager (similar to adept). It installs, but more reliably. It's also much more compatible with the BSD system underlying the iPhone.
2. Do not install the BSD subsystem package. Cydia has its own version of the stuff.
3. You can still use Installer if you want, but Cydia will contain many of the same packages.
4. Install Bosstools immediately after Cydia, and then use it to "make more space for apps". It changes the path name used for installing applications, which in turn puts them in the large partition on your iPhone. If that means nothing to you, don't worry, just do it.
5. Remember to sync your iPhone on a regular basis, to avoid the hassle of recreating stuff. You never know when an app is gonna brick your phone.
6. I have yet to see a killer app for the iPhone, other than Safari which you get even if you don't Jailbreak.