Well I'd hope for a slightly better range than 20Khz and maybe resolution. Also I'd imagine the noise level wouldn't be very satisfactory.

With a 3.5ghz oscilloscope you could work on Mhz order chips, power supplies and who knows what other fun stuff.

I figured you were just looking for something to toy with. I figure that turning this device into a scope is not going to result in an accurate scope nor something that would be useful beyond entertainment value.

It seemed like a good idea to recommend something cheaper, easier, and better documented. Besides, who doesn't want to use their mic jack as an oscilloscope? ;-)