I am new here but was compelled to add this solution as I have seen several different suggestions on how to use your own incoming text message notification, none of which seemed to work for me, also they weren't exactly in easy to understand terms for those users who are less techy minded.
So here's my solution in easy to understand step by step fomat.
1) First make sure you have the tune or song you wish to use on your phone.
2) Select 'Application' from the Applications screen.
3) Select 'My Files' - when the my files screen opens it will be shown on the top left as 'sdcard'
4) Select the 'Media' folder
5) Click the menu symbol bottom left and select 'Create folder'
6) Call the folder 'Audio' and select it
7) In this folder click the menu symbol and select 'Create folder'
8) Call the folder 'Notifications'
9) Now go to the folder that contains the tune or song you wish to use as the text notification
10) Select 'Menu' bottom left, select 'More', select 'Move'
11) Select the song/tune you wish to use and select 'Move'
12) Next select the 'Media' folder, select the 'Audio' folder, select the 'Notifications' folder and then select 'Move Here'
13) Go back to the screen that shows all your applications, select 'Applications' icon, select 'Messaging', select 'Menu' and then 'settings'
14) Scroll down to the bottom of the screen and under 'Notification settings' select 'Select ringtone'
15) Here scroll through the list and find then select the track you wish to use, make sure the 'green dot' is in the circle next to it, click ok
There you go, that should now be done.
One final tip, if this did not work straight away turn your phone off and then on again and it should now work.