How to set SMS ring tone on Sony Ericsson LT18i?

Open the settings menu in your phone - open applications - open management applications. Find the Android ringtone system in the All column. After opening it, find Clear Default Settings and click on it. After the setting is completed, go to Settings - Notification Ringtone in Sound. After clicking, there will be two options. One is the Android ringtone system and the other is the sound selector. Select the latter to set a custom ringtone.