JamVM classes outside core java on iPhone

Question

So I have an old iPhone (first generation) laying around, and I thought I could use it to do some fun stuff. I jailbroke it, and installed the Java package off cydia. However, whenever I try to use any classes that are outside of core java (anything that has to be imported), I get a no class def found error. Printlns and simple arithmetic work, but nothing much else. I get the same error doing the same thing on my first gen iPad. Has anyone else played around with JamVM and gotten anything outside of core Java to work to work?