While driving, I wondered if the new iPhone 3G S had to be oriented with the screen parallel to the ground for the magnetometer to work properly, like a traditional compass.  This functionality is supposed to enhance the upcoming turn-by-turn GPS apps where a phone is clamped so that the screen is perpendicular to the ground.  But will the magnetometer still function properly?  Well instead of Googling, I put it to the test.  Not only does the magnetometer function as desired when the phone is held vertically but also when tilted to almost 45 degrees past vertical before the Maps app rotates 180 degrees.  Try it out.

While testing, another question came to mind: Will this work in landscape mode?  After testing, I found that the compass doesn’t work as expected in Maps.  When landscaped, the compass points in whatever direction the headphone jack is pointing regardless of whether the screen is parallel or perpendicular to the ground.  However, in the TomTom app demo, it seems to work properly in either portrait or landscape mode.  So it looks like a software limitation in Maps, not a hardware fault of the 3G S.  Not a big deal unless you want to use Maps as a free, bird’s-eye, landscape GPS app until TomTom and others release their apps for sale.