Connecting to the command line:
The first step is to jailbreak your phone. Jesus's guide will get you started with both AppTapp for Mac and iBrickr for Windows. They're both just as good. If you're on Windows and using iBrickr, you have to go to the extra step of installing Installer.app onto your phone. You can do this inside the Applications section of iBrickr.

Now, open up Installer on your iPhone and install the "BSD Subsystem", "Community Sources", and "OpenSSH". OpenSSH installs the program that lets you connect onto the iPhone remotely, and BSD Subsystem gets you some command line tools on the phone itself to do some file manipulation. Once done, turn your phone off and on (just to be safe) and you should be ready to connect.

Next, connect to your home's Wi-Fi network and find out what your iPhone's IP Address is. It should be listed under the clients section of your router's configuration pages. An even easier way is to look in your Settings App, under the Wi-Fi network you're currently connected to. [Thanks Ravi!]

If you're on a Mac, you already have a built-in SSH client. If you're in Windows, you can use Putty. Now, open up Terminal (Mac) or Putty (Windows) and connect to your iPhone.

On Mac, just type in "ssh root@IPADDRESS" without the quotes. Accept any authentication requests that pop up. Type in "dottie" as the password when prompted.

On Windows, enter in the IP Address into the "Host Name (or IP Address)" in putty and hit Open. Accept any authentication dialogues that pop up. Log in as "root" when prompted, with the password "dottie".

Once you're in, you can move around freely with these command line basics.

If you have programs like Erica's Tools installed, you can even take screenshots and copy them onto your desktop.

Copying Files:
Although you can easily copy files from the command line, the easiest way is to do it graphically with an SFTP client. On Mac, you can use Transmit. On the PC, there's WinSCP. The basics are the same, Just enter in your IP address, the login (root), and password (dottie). Now you can drag and drop files to and from your phone easily.

Changing your password:
If you enable SSH on your phone, you should change the password from "dottie" as soon as possible, otherwise people can easily get into your phone and find out what horrible, horrible taste in music you have.

Just log in to your iPhone, then type "passwd". You'll be prompted to enter in the new password. Thanks Premek, I didn't know it was installed!

Deprecated instructions below:

On Mac, type in:
perl -e 'print crypt("MYPASSWORD", "XU");'
Where "XU" is a random two letter combination to randomize your password a little more.

On Windows, you'll have to download and install perl before you run that command. (This is a stupid way to do it. Does anyone know of an online generator or an easier way for Windows?)

Once you have your new encrypted password from the output of that command, copy the file /etc/master.passwd from your iPhone onto your computer, and replace the root password in the file. The relevant line looks like this:

root:XXXXXXXXXXXXX:0:0::0:0:System Administrator:/var/root:/bin/sh

Replace only the X's with your new encrypted password, making sure not to mess up the colons, and upload this back into your phone under /etc/master.passwd Now, reboot the phone. Your new password should be in place.

That's it! If you have any questions or see any holes, make a comment.

Options that require Jailbreak
• SSH/File Transfer: All you have to do is drop an iPhone's iPod-compatible ringtone into the /Library/Ringtones directory, meaning you can use MP3s, AACs (protected and unprotected), or M4As. Anything that your iPhone's iPod supports will work.
• iBrickr (Windows): iBrickr actually transcodes your sound files for you, so if you're looking up old WAV sound pages from 1999, iBrickr can convert them into something that the iPhone understands before syncing. [iBrickr]
• iFuntastic (Mac): Same as the SSH/File Transfer option. Just drag them into the correct /Library/Ringtones folder. [iFuntastic]
• Sendsong: Allows you to pick any song from your iPod and move it into the Ringtones section. Install this with AppTapp.

Options that don't require Jailbreak
• iTunes Music Store: You can manually place AAC files into the correct iTunes Ringtones folder as long as it has the right file extension. Works with purchased iTunes songs or songs you've converted to AAC format. [JoeMaller]
• Rogue Ameoba's MakeiPhoneRingtone (Mac): This takes advantage of the iTunes 7.4 and iTunes 7.4.1 ringtone file compatibility workaround to get the Ringtones show up in iTunes. All you have to do is drop in an AAC file, which can be one of your songs purchased from iTunes. [MakeiPhoneRingtone]
• iToner (Mac): Copies ringtones to your iPhone, bypassing iTunes, should be guaranteed to work with future iPhone updates. Costs $15. [iToner]
• iPhoneRingToneMaker (Windows): Transfers ringtones to your iPhone, but lets you edit them beforehand in its editor so you can chop down long songs to a manageable clip. [efksoft]

We recommend you use one of the free methods, since they're actually quite easy to do. Even if you don't want to jailbreak your phone, the iTunes Music Store manual method and Rogue Amoeba's MakeiPhoneRingtone can take care of this for free. But if you want to make sure your ringtones don't get deleted when a new version of iTunes or iPhone Firmware comes out, you may want to try jailbreaking and placing the songs into the ringtones folder manually.

Obligatory iPhone Book Whoring: These iPhone Ringtone features are covered in my book, How to Do Everything With Your iPhone, along with hacking, cracking, and much more. Don't worry, that cover is going to be changed. Soon. *Sends nagging email to publishers*

Additional research by Benny Goldman