Do you ever wish you could listen to your entire music library on your iPhone or iPod Touch, not just the tunes that fit in memory? That's the idea behind AudioIn, which turns your PC into a music server that streams songs via Wi-Fi.
Yep, it's Wi-Fi only, meaning it's suitable for only around the house. And what's wrong with that? AudioIn works much like Apple's AirPort Express, except that instead of tying you to one room, it lets you move around.
To use the $4.99 application, you must first install AudioServer, which, for now, is a Vista-only utility. (It should work on XP as well, but for some reason the developer says it "may not.") Once up and running, AudioServer captures the audio from iTunes, Windows Media Player, or just about any other source, then streams it to your device.
However, don't mistake AudioIn for a Sonos-like music-library manager. Out of the box, this application offers nothing more than play/pause controls and a volume slider. You can't view your library, choose which songs or artists to play, or even skip tracks.
Actually, you can skip tracks if you don't mind a little tweaking: AudioIn lets you configure up to 18 control buttons to reproduce keyboard commands. So if you want a next-track control for iTunes, for instance, just program a button to be Ctrl-Right. It's a hassle, but it works.
Another hassle: AudioIn requires headphones. For whatever reason, it can't reproduce tunes through the iPhone/Touch speaker.
Ironically, AudioIn's interface looks like a big speaker--but it's not. It's actually meant to represent a trackpad, and sure enough, you can drag your finger around it to remotely control your mouse cursor. Given that AudioIn's purpose in life is to free you from your PC, I'm not sure I see the point of this capability.
If you're not interested in that feature and don't want the programmable buttons, AudioInLite is a little more reasonable at $2.99. (There's also a free version that limits you to 60 seconds of playback, just so you can test the waters.)
In my tests, AudioIn worked as advertised, streaming non-DRM songs at a quality that I'd describe as "pretty good." It's definitely a nice little application to have when you're doing household chores, chilling on the patio, or otherwise away from your PC.
But it's also annoyingly limited, with a quirky interface and slightly out-of-whack price. I think most users would be better off with Simplify Media, a similar application that's iTunes-only but much more robust.