Here’s an idea for all you iPod/iPhone developers, and all I want out of it is a free unit.

More and more often, I play my iPhone through my car stereo system, using a cassette adapter from the great folks at OtherWorld Computing. When I get a phone call, the podcast that’s currently playing fades out and I hear my call through the car speakers, which sounds great. The problem is that when something is plugged into the headset jack, the iPhone’s built-in mic is disabled. What I would love to have is a little dongle that plugs into the headset jack, contains an in-line microphone, and has a jack at the end into which I could plug my cassette adapter. That way, I’d had a speakerphone built into my car stereo.

Does such a device exist already? If so, please let me know. If not, you heard it here first.

UPDATE: It looks like Monster may have come up with just the device I’m looking for. $20 seems a fair price, too. Surprising, given their pricing on high-end cables.