The iPhone is wonderful, except when it isn't. Beautiful, great functionality, wonderful applications.. but have a problem and it can quickly be frustrating. It's almost like Apple tried to make the appearance of there never being problems with this wonderful gizmo. Troubleshooting problems is made harder because the beautiful interface isn't cluttered with the details you need to learn what might be the problem. Whatever.. that's me ranting and what brought me to this rant is how Apple makes it hard to troubleshoot iphone sync problems. A few months ago, upon plugging my iPhone into my computer iTunes would give me a warning dialog about being unable to recognize the device along with an eminently unuseful hex code. A week or so after that iTunes stopped seeing that the phone was plugged in. This is one of those annoying things that I left on the back burner until last week when I wanted to get to the bottom of it, leading me on the journey to troubleshoot iphone sync problems.
Apple's knowledge base is a wealth of information but this specific iphone sync troubleshooting problem is not really discussed. Unfortunately. Also it doesn't appear anybody on Apple's user-discussion forums are having this exact issue. Fortunately there is a thread of diagnosing and troubleshooting information which I was able to follow, and in my case not reach a successful conclusion.
My exact symtompology is that the iPhone 3GS is not recognized by the computer I want to sync it with. That computer has no problem with recognizing and syncing with my iPad but the iPhone, no go. Fortunately the iPhone does get recognized and syncs with the iTunes on my MacBook Pro, but that's starting to get ahead of the story.
The first place to stop is either iPhone, iPad, or iPod touch: Device not recognized in iTunes for Windows or iPhone, iPad, iPod touch: Device not recognized in iTunes for Mac OS X depending on the operating system of your desktop computer. Apparently in Apples view of the world there is only Mac or Windows, and they don't recognize the existence of Linux. But if you're using Linux you're already aware of this.
The directions here are pretty obvious. Is the widget fully charged? Is it plugged in to a USB port on the computer? Is the cord fully seated? Restart both the device and the desktop computer. Try plugging the cord into a different USB port.
Those are all obvious things to try that one might or might not think of depending on their state of franticness.
It pays to be aware of the basic system requirements of what desktop computers can run the version of iTunes required to work with your iDevice.
The iPhone: Basic troubleshooting page is useful if the device is not in a state of basic functioning. That is, maybe it doesn't even turn on etc..
In my case the phone itself is working, it turns on, fully functional, just not recognized by the computer. Restarting the computer doesn't help, neither does restarting the iPhone.
There's a rather drastic step to take, iTunes: How to remove and reinstall the Apple Mobile Device Service on Mac OS X.
This step completely removes iTunes and various operating system modules that interface with mobile devices. It has you go to specific folders in /System and /Library, and remove kernel extensions which are installed along with iTunes. This is part of completely removing iTunes from your computer.
Obviously the hope is that perhaps something got corrupted in these kernel extensions, and by completely removing them it'll reset the computer to a known state.
After removing the kernel extensions (and rebooting twice) you're instructed to download a new copy of iTunes and install it. (and reboot at least once more) Theoretically the phone will be recognized after that, and all will be pink and rosy and wonderful and we'll go dancing into the night. Unfortunately that did not happen for me.
I had a huge concern before taking this step about whether my iTunes library would be lost. I've bought several things like movies and iPhone/iPad/etc applications and didn't want to lose them. Good news is the iTunes library was not lost.
The iTunes library (by default) lives within the ~/Music/iTunes folder. Simply leave that folder in place. The instructions do not say to remove that folder, so leave it there. After reinstalling iTunes and launching it your old library will pop right up and that part of this process was fine.