Further Complication
I imagine it would be further complicated by what country you are in and what laws you are subject to as well.
I believe that Lucasarts made a big deal about that and had one of the iPhone Star Wars Soundboards taken down and then they partnered with THQ to actually create a board that they now sell on the AppStore.
For our soundboard application, because of all the user generated content that is available, we take a YouTube approach to the whole situation, and if you upload something that infringes on copyright and someone complains we will just delete it. We can't control what people are going to submit, nor can we screen it for illicit comment on the way in, so unfortunately there is no other way to do it.