I'm looking at buying a new car. Many of the cars I see now come "standard" with an audio-in jack. The option of a Bluetooth connection is usually much more expensive. My question is: If I plug my phone into the audio-in jack with a cable to the headphones port, can I use the phone "handsfree" effectively while operating the vehicle? That is, will the incoming sound come over the speakers, and not echo hopelessly into the input on the phone itself? Or do I basically have to spring for the Bluetooth, either at purchase time or aftermarket?
I have tried to do this in my own car - here's my experience with it.
From a "hearing the person" perspective, the headphone jack into the car's speaker system works great. What's even better is that the person doesn't (generally) hear themselves talking either (no echo or feedback). This is using an original Moto Droid, so your mileage may vary.
The problem that I have with this kind of setup is having the person hear me. I still, generally, have to hold the phone up to my mouth for the person on the other side to understand what I am saying. I have found it helps a little bit to enable speaker phone, but then the person sometimes gets the echo feedback. It's really a no-win situation.
Most likely, you'll have to get an aftermarket blue tooth headset.
It's possible to use it this way but the quality of the results are going to depend on your phone, the car and how loud you have the speakers.
I have done something similar with my Moto Droid 1 and will share my experience:
The only difference between my configuration and the one you are inquiring about was that instead of plugging directly into an audio jack in my car I used an FM transmitter that I plugged into my headphone jack on my phone (which then wirelessly beamed the phones audio to 88.1 FM on my stereo). In the past I have done the same thing with a tape deck adapter. Needless to say the result was that all audio on my phone was coming out of my car speakers. I did this to listen to music and podcasts and accidentally discovered the hands free component when I got a call while it was hooked up this way.
Needless to say I was surprised to find that there was no feedback loop, no echo, and the person on the other end couldn't hear the speakers at all. It was also reported to me by the person on the other end of the line that my microphone was picking up my voice just fine, even though the Droid was sitting in my cup holder. None of this really seem logical to me but it worked. That being said I don't know how a different phone would respond with a different car. I suggest that you bring a male to male 3.5 in headphone cord when you test drive the vehicle and place a test call to someone you've already briefed on the situation, so they can help you evaluate the quality of the call.