It looks like my german post for own sms tone for your iPhone is very popular particularly regarding since the new 3G iPhone is on the european market. So I translate this post in english… or I’ll try it. 
Here is my little manual, which I found somewhere in the internet, to make your own sms tones. All you need is you own iPhone, some nice music/effects/anything other and iTunes!
- Choose a favorite MP3 files and cut out some seconds (2-3 seconds should be enough)
- Now import this MP3 in your iTunes and convert it to a AIFF file
- Copy this new created AIFF file on your desktop
If you don’t find this file, look at the properties of the file in iTunes – there should be the path where it’s located on your harddrive. - Now change the ending *.aif in *.caf
- Now connect via SCP on your iPhone (Mac: Cyberduck, Win: WinSCP)
- Go to “/System/Library/Audio/UISounds”
- Here you can change one or all of the default sms tones.
But create first a backup of the file which you’ll replace! e.g. rename “sms-received6.caf” in “sms-received_6.caf” and then copy your new file to “sms-received_6.caf”.
And here is which file corresponds to which name:
sms-received1.caf -> Tri-tone
sms-received2.caf -> Chime
sms-received3.caf -> Glass
sms-received4.caf -> Horn
sms-received5.caf -> Bell
sms-received6.caf -> Electronic
Not working? Did you all right? Check these points:
- was it a AIFF file?
- shorter than 30 seconds?
- Did you converted a MP3 to an AIFF file via iTunes?
- Did you replace the right file on your iPhone?
- Did you really copy the file on your iPhone?
Now have fun with your new sms tones.