Custom Ring Tones, Notification Sound, alarms but not SMS
To use custom ringtones for your phone ringtone, your alarm or your text message notification, simply copy an MP3 file to one of the following folders:
If they don't already exist, then create a new folder.
The file will then show up when you want to change your ringtones.
For Ringtones go to Settings - Sound - Phone ringtone
For Text Messages go to - Settings - Sound - Notification ringtone
For Alarm, set the sound when you add a new alarm
Does not seem to be a way to customise SMS tones