Is there an iPhone dock with a headset jack?

Does anyone know of a dock for an iPhone that has standard usb data/power, but also a headset jack (not just speaker / headphones output)?

I wonder what is that for, if it's to connect to a stereo, the jack on the Universal Dock is more than enough.

If the idea is to use the phone to answer calls while in the dock, I would strongly suggest a Bluetooth set as that's what they are made for. You will find plenty on the Apple Store as well.

The biggest problem you face here is the fact that you want to use your phone, as a phone, while in a dock.

First problem:
Many docks are "not compatible" with the iPhone, they don't have GSM noise filters on their speakers, so if you dock it and listen to music, you get that god awful chirping when the GSM radio starts going.

Second problem:
Those that are, make data connections, not line-out connections! The only way to fulfill this request is;

• if the chosen dock connects not only via data, but ALSO via the headphone jack, and;
• that connection is a triple-ring connection, just like the iPhone headphones. Note that you're highly unlikely to find this, because docks are for data/playing audio (which can be accomplished via the audio jack), the "dock your phone and use the computer as a gateway to phone functions" use case is, unfortunately, not present.

Third problem:
The iPhone is too smart. A while back I was driving with my phone plugged into a line-in port on my car (for music), and I was received a phone call. I had guests in the car, all friends, and figured I would just let the conversation take place via the car stereo, and turn on speaker so the other part could adequately hear me. No such luck. When not on speaker, the call came out of the ear piece only, when on speaker, the call came out of the speaker ports. The iPhone will only use the headphone port for a call if it has a microphone attached.

BluePhone Elite was an option for this (with serious caveats), but it never had terribly good support for the iPhone. Only because of the limitations imposed by Apple. And, apparently BPE is dead now? What a shame. That was a good app for many many other phones.

I'm (unfortunately) very confident in saying that you will have a very hard time finding this dream product of yours, and you're better off simply plugging your own headset into the headphone port, or like balexandre suggested, pair a Bluetooth headset. A product like you want will invariably not pass Apple Certification, which means you will not easily find it in any mainstream store (not only Apple Stores, but BestBuy and it's ilk).