Q: I was recently reading your article, The Complete Guide to iPhone Car Integration. I have a car with an auxiliary in port. I was wondering if you could tell me how the phone feature will work if I set it up this way. Will the caller come through on my car speakers, and will the mic on the actual phone still work, and will it pick up my voice?
A: If you connect your iPhone to the AUX in port on your car via the iPhone’s headphone jack, then all of the audio from your iPhone will come through your car’s speakers in much the same way as it would through a set of headphones. This includes your iPod playback, phone call audio, and other sounds emitted by the iPhone such as ring tones, alarms, e-mail notifications, and so forth. In this configuration, the iPhone volume controls are also applied, so you may need to adjust the volume on both your iPhone and your car stereo for optimal listening levels.
When connecting an output-only device such as speakers, headphones, or an AUX cable to the iPhone headphone jack, the iPhone’s normal microphone remains active during phone calls, so you can in fact listen to your phone call through the car speakers and speak through the iPhone mic. Note, however, that the iPhone is not designed to handle echo cancellation in this configuration, so your callers on the other end may hear an echo of their own voice being fed back to them as a result of the audio from your car speakers also being picked up by the iPhone mic. Further, how well the actual iPhone mic picks up your voice will depend largely on the ambient noise of your car and where you choose to place the iPhone. Enabling speakerphone on the iPhone will improve the mic range, but will also direct your call audio out via the iPhone’s internal speaker rather than your car stereo. Keep in mind that actual car handsfree kits are specifically designed to address these type of issues with features like echo and noise cancellation.
Note that if you’re using the iPhone’s Dock Connector to tie into your car stereo system, then only your iPod audio will play through the car stereo at a fixed volume level output from the iPhone. In this configuration, phone calls still come through the iPhone handset, speakerphone, or via any Bluetooth hands-free accessory that you might be using. This is generally the recommended configuration, ideally paired with a handsfree Bluetooth accessory such as a headset or in-car kit like the Counter SurfaceSound Compact (iLounge Rating: A-). With this setup, your iPod audio will play through your car stereo system, and when a call comes in, the iPod audio is automatically faded down and muted by the iPhone and the incoming phone call is handled by the Bluetooth accessory. When you complete your phone call, the iPod music is resumed by fading back up to its previous volume.