The current model for the 3GS isn't quite as impressive as the new model -- it's just basically got a volume control (though the audio heard through headphones does sound really clear and loud). But the iPhone 4 model (of which we only saw a prototype on the show floor -- the real thing "will probably be thinner," according to VentureCraft, and should be ready to ship around April) is really interesting. It has digital audio output, and can send it through a optical cable in either 96k/24bit or 48k sampling rate (adjusted via a toggle). That means you can use the DAC port to kick out audio to a home theater system directly from the iPhone itself, and because the amp is running, it'll sound that much better. The frequency response is listed as 10 Hz to 120 kHz and suitable headphone impedance is listed as 16-100 ohms. The op-amp is a Texas Instruments/Burr-Brown running on each channel, which all adds up to some pristine digital audio output.
These are billed as battery chargers as well, but we suspect they may be more of a drain than a dedicated battery -- while you use the amp, you'll probably need to just keep it plugged in. The unit isn't cheap -- the 3GS version (without optical) runs $199 shipped from Japan, and the iPhone 4 version will probably be somewhere between $300-350. That is shipped, VentureCraft told us -- no extra charge, even though the unit is coming from Japan. But come April when this thing is ready, the right user might find it just what they need.
We've got a quick video from the booth on the next page.