Access our platform on your iPhone. Then tap on the Upload File button to select the MP3 file you want to convert. Alternatively, drag and drop it into the upload area. Choose M4R as the target format from the drop-down list. After that, press the Convert button to turn MP3 into ringtone file format for your iPhone (M4R - the custom iPhone ringtone format from Apple iTunes). After the conversion, tap on the Download button to save the newly fresh M4R file.