I generally use my HiJack on an iPhone, but just tried it on several devices because of a question I got. In all cases, I tried both the free HiJack Oscilloscope app and techBASIC. The results were the same with both applications, so I think this is a hardware issue.
iPhone 4: Worked
iPhone 4 (different physical device): Worked
iPad 1: Did not work
iPad 2: Did not work
iPad 3: Did not work
Has anyone had success with the iPad? Did the extension cable idea work?