Why go with half-measures ? Go with classic grindcore instead. In fact, Napalm Death's seminal album "Scum" has pieces short enough for both ringtones and message notifications!

For example, use "You Suffer" (3 seconds) for IM notifications, "Common Enemy" (16 seconds) for messages and "Pseudo Youth" (42 seconds) for a ringtone

P.s. I don't use those but come to think of it I may have to, lol,