If you want to give your mobile phone a unique sonido de iphone, then downloading and customizing ringtones is a great way to do so. There are a number of free websites that offer a wide variety of ringtones. Some of them are categorized, and you can find the perfect one for your phone by searching by category or popularity. Other sites will let you choose the ringtone you want, and then download it to your phone with a click.
You can also download free apps that allow you to create ringtones right on your phone. One of these is the Should app, which offers an extensive catalog of ringtones for your iPhone. The app is compatible with the iPhone 3GS and 7+, and has a nice user interface.