To change your ringtone on iPhone 3GS without using iTunes, you need use CDs, DVDs or data files. Then, you can download "iPhone Ringtone" Maker tool. It allows you to change your ringtone by clicking the "Browse" button to access the songs that are in the data files. Drag and drop the slider for music to be converted. Find more details from http://www.xilisoft.com/iphone-ringtone-maker/how-to-create-ringtone-for-iphone.html.