What he is saying is that your device is not capable of playing mp3's. You can set a mp3 as a ringtone. To download it you'll have to host it on the web and download it w/ your bb browser.
BB devices I've owned: 957 : 7750 : 7250 : 8703e : 8830 : 9530 : 9630 : 9650 : 9930 : 64GB PB
BES 5.0.4 ~ BES 10.1