Sharon has an 02 XDA Mini and we've been trying to change to notification sound that is played when she gets a text message. However, there's very little guidance on how to do it, and what guidance there is doesn't seem to apply to the XDA Mini that Sharon has.
Firstly, the sound file you want to use has to be a ".wav" file.
Using the phone's "File Explorer" (or your PC's using a USB link), paste a copy of the sound file into the "/Windows" directory.
From the start menu choose "Settings". Under the "Personal" tab click on "Sounds and Notifications" and then select the "Notifications" tab.
From the "Event:" drop down list choose the event that you wish to change the notification sound for. For text messages it is (obviously) "Messaging: New text message".
In the drop down list immediately below that you should then be able to find and select the name of the sound file that you wish to use.
We had real problems changing the sound initially because we didn't realise that the sound file had to be a ".wav" file.
We've moved! theaardvark has a new home at www.theaardvark.co.uk