using downloaded tones in Samsung galaxy Ace


hey,I own a Samsung Galaxy Ace. Just downloaded a ringtone(the one which says TAXI!) from the net in MP3 format and saved it in my SD card.I would like to use it as a message received alarm.Tried to aproach it in several ways to no avail.I know that this tone is originaly from NOKIA so maybe there is an incompatibility issue here.Tks for help