These instructions were contributed by "Christian" "Ksilebo", and "TkN". For the ultimate in customization, you can follow these steps to change your system sounds for new mail, new sms, new voicemail, et cetera. Remember you will be updating the system sounds, you can always restore them with a full restore or one by one by using the backups in the 39.dmg file.
The default system files in /System/Library/Audio/UISounds
alarm.caf
dtmf-2.caf
beep-beep.caf
dtmf-0.caf
dtmf-1.caf
dtmf-3.caf
dtmf-4.caf
dtmf-5.caf
dtmf-6.caf
dtmf-7.caf
dtmf-8.caf
dtmf-9.caf
dtmf-pound.caf
dtmf-star.caf
lock.caf
long_low_short_high.caf
low_power.caf
mail-sent.caf
middle_9_short_double_low.caf
new-mail.caf
photoShutter.caf
ReceivedMessage.caf
RingerChanged.caf
SentMessage.caf
short_double_high.caf
short_double_low.caf
short_low_high.caf
SIMToolkitCallDropped.caf
SIMToolkitGeneralBeep.caf
SIMToolkitNegativeACK.caf
SIMToolkitPositiveACK.caf
SIMToolkitSMS.caf
sms-received.caf
Tink.caf
Tock.caf
unlock.caf
ussd.caf
Voicemail.caf
Step 1
Choose a file, convert it to .aif using QuickTime and rename the .aif to .caf. The .caf sould have the exact same name as the system file you are trying to replace (i.e. yourCustom.aif becomes new-mail.caf).
Step 2
Put the new .caf file in the phonedmg folder used earlier.
Step 3
In the Terminal type: putfile /System/Library/Audio/UISounds/name of whatever you are changing.caf Then press the enter key.
http://www.hacktheiphone.com/iphone_ringtone_installation_windows.html
Make sure you are converting it right or you will not hear the sound or your iphoneinterface will crash.
First: Use Quicktime and Choose A File...[Size of the file don't matter? I am using full songs]
Second: Export The File
Third: Rename the file to .caf [Note: you must rename the .caf here..not anywhere else]
Make sure the File is right..