Your default sonnerie telephone is selected for you by the manufacturer when you first purchase your device, but it is possible to customize your own. You can do this with your own music files or by downloading a free app that lets you create a custom ringtone.
There are many ways to customize your ringtone, from using a simple music player to editing an entire song file. There are also apps that allow you to add a short audio clip as a ringtone.
You can also set a different ringtone for each contact on your phone. This is especially useful if you have a group of friends or family members that you often text with.