If you've been wanting to activate your iPhone without iTunes so you can use a non-iPhone AT&T/Cingular SIM, or you just want to use your iPhone as an iPhonePod, I have some good news for you. The guys over at ModMyiPhone have introduced a program that doesn't require you to work from the command line.
Not everyone loves the command line. It's a basic fact. And, for those of you who have been waiting for a real application that avoids using Terminal commands, point your web browser at this page. iActivator wraps a GUI around iPhone activation, and makes it simple to use the jailbreak, iASign and iPhoneInterface tools.
For those of you still worried about turning your iPhone into an iBrick, keep in mind that this is still early software. You may want to wait a few weeks for the software (and the hacking tools that underlie the application) to gain stability. Also, be aware that the public link seems to be down. You may have to sign up for a (free) account before being allowed to download the members-only version. A final note: it's unclear whether this is a Universal binary solution or (as I'm guessing) Intel-only.