Install Phonezap in your iPhone and you're ready to go. You can actually do it with your iTunes as well, just RTFM!!!

Customise the conversion setting by the screen resolution, bitrate & the audio bitrate, those will affect the size and quality of a converted movie format.

480x320 screen resolution, video bitrate: 1000(or lower if you want smaller file size), Fram rate: 29.97, Audio Bitrate: 56 (or lower), Sample Rate: 48000 & Channel: 2 (Stereo).

If you follow the settings above it will be good enough for a DVD or movie conversion.

Here's another iPhone trick where you can play the mono music through your existing Bluetooth headset with a simple little change in your audio output options:
1) Pair your Bluetooth headset with your iPhone - we're not gonna get into the specifics, just do it.
2) Go to your Voicemail and hit the "Audio" button (when the iPhone is not paired with a headset, this button will say "Speaker."
3) Choose your headset in the subsequent audio selection dialog.
4) Get to your homescreen and hit the iPod icon.
5) Start playing a song and revel in the Bluetooth headset

Inform me if this been posted before and I will delete this post.

This post has been edited by Joelles: Jul 10 2008, 12:42 PM

FYI, customizing ringtones can be done directly from your iPhone by choosing your song from your iPod. Just Install Phonezap(for ringtones) or "Ringtones"(for ringtones & message tones).