The iPhone comes with a built-in notification alert tool, which notifies you of a new SMS (text message). It's helpful because it enables you to view an incoming message on time. To notify you of a new text message, an iPhone relies on a number of sounds, which are all distinct in nature. Using the tune that you want, you can change your SMS alert.
Turn on your iPhone and tap the "Settings" icon on the main menu to launch the settings console.
Tap the "Sounds" button to launch the sound settings window. Tap "New Text Message." A new window launches with a variety of sounds that you can use as a new SMS notification. Tap the sound that that you want to use.
Tap the "Sounds" button on the top-left corner and tap "Settings." Tap "Messages" and tap the "Repeat Alert" button if you want your iPhone to notify you repeatedly of a new SMS message.