Created by Apple, the M4R file type is utilized to produce custom ringtones on the iPhone. While ringtones bought through the Apple store in iTunes are automatically added to a user's iTunes library, third-party ringtones must be manually added to the user's iTunes library. Once added to the library, an M4R file is displayed in the "Ringtones" library shown in the left side bar of iTunes. Although ringtones are loaded to an iPhone in a similar manner as music files, they are not displayed in the device's "iPod" application and can only be seen in the ringtones settings menu.
Connect your iPhone to your computer using the device's USB connector cable and launch iTunes if the application does not automatically start.
Click "File" in the menu bar of the iTunes application window and select "Add to Library."
Use the "Add to Library" dialog box to find the M4R that you want to transfer to your iPhone. The M4R file is located where you saved it on your computer.
Click the M4R file in the "Add to Library" dialog box and click the "Choose" button.
Click "Ringtones" in the left side bar of iTunes.
Click, drag and drop the M4R file from the "Ringtones" library window pane to the iPhone icon displayed in the left side bar. ITunes transfers the ringtone file to your iPhone.
Access the M4R ringtone file by going to “Settings,” tapping “Sounds” and tapping “Ringtone.” The M4R file is shown in the list of ringtones.