So I’ve had my new iPhone for 4 days now, and I’ve discovered a big issue; for me at least. It seems that the compass is very sensitive to magnets, such as those in speakers (e.g. speakers in your car’s dashboard and door panels). In my previous 3Gs review, I mentioned a problem with the Google Maps app not tracking GPS and compass simultaneously. As it turns out, it was the magnetic interference that was at issue. Here’s a link to Apple’s response; this is relevant part:
For example, your car’s dashboard may have a high level of magnetic interference. If you wish to mount iPhone 3G S on a car’s dashboard and use Compass or Maps, do not wave the device in a figure 8 to calibrate. Instead, mount iPhone 3G S, open Compass or Maps, and disregard the message to calibrate. iPhone 3G S will eventually re-calibrate after several turns. Note that it may need to periodically recalibrate while you are driving, depending on the level of magnetic interference present where you have it mounted.
So it seems that Apple is downplaying the issue. I wonder why the compass built into my car’s dashboard is not affected by magnets.
