I have approximately 4000 audio recordings in my iTunes Music Library that take up about 17 gigabytes of disc space.
Needless to say, I can only store a subset of my music library on my iPhone. On a recent trip, I listened to one of my music playlists over my car stereo. I noticed that the tracks played back in random order and not how they were listed on my device. It took a while, but I eventually figured out that the shuffle switch on my iPhone was turned on.
What puzzled me was figuring out how to deactivate the shuffle option. The obvious choice — the iPod Settings menu — provided no clues.
After surfing the Internet, I eventually found the solution from a cryptic reference included on page 63 of the iPhone User Guide. During music playback with shuffling turned on, the Shuffle control icon (the one with the intersecting arrows) is highlighted in blue. Clicking once on the icon changes its highlight color back to white and allows the songs to play back in their original order.