Fix!
I am getting the exact same thing at work. It will charge on the car charger, but not when plugged into the Mac -- no charge, no sync. I brought the car charger inside and plugged it into the Mac -- still nothing.
I tried restarting the phone. Nothing, but it's stuck on "Searching..." for network. This was a soft reboot (just turning the phone off manually, and turning it back on).
Trying a hard reboot now (holding home and power until phone cycles off, and then comes back to the Apple screen).
Okay, great! now the phone is not coming back up at all -- it has been stuck on the Apple screen for about 10 minutes now!
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Okay, it finally came back up, it can see the AT&T network, but it still will not sync or charge while plugged into the Mac.
Message was edited by: Claidheamdanns, to remark that the phone finally booted back up, after about 10 minutes.
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Okay, I finally got a solution that worked. I downloaded the latest version of AppleJack, a free utility that does a deep clean on your Mac, repairing preferences and the like, better than any other utility I've used.
You must use it in Single User UNIX mode, but this is no reason to fear it. Just hold down Command+S after the gong, when you reboot your computer. When you start seeing white text on a black background, you can let go. When the text stops scrolling, type this command at the prompt:
applejack auto restart
and hit the return key.
This tells AppleJack to run all it's routines automatically, and then reboot your Mac in OS X. It can take a little while to do it's repairs if you have a big drive. It took about 15 min. on my 500GB drive.
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When it completed its tasks and rebooted, I plugged the iPhone into it's doc and it now works like a charm, syncing as we speak, and charging!