Like I said above, he is (since his first couple shorts are in the public domain). The trademark on Oswald expired too.
I wouldn't bother making new Oswald cartoons (or even distributing the old ones), because Disney's lawyers have been known to go after people who are within their legal rights on public domain characters (they went after someone who was selling public domain comic reprints of Mickey Mouse comics even though they were just called The Uncensored Mouse with a black cover that didn't even mention Mickey Mouse. Disney won that case, because Mickey Mouse's first cartoon is still copyrighted (which is actually in question in academic circles, but Disney is vicious in protecting their copyrights, so it has never been contested in court).
I'd personally love to make a new Oswald cartoon, but it'd be a real David vs. Goliath fight going against a corporation as big as Disney.