Currently Being ModeratedJul 20, 2013 1:20 PM (in response to DFSYHM)
If Apple has replaced your device and it still will not work, however other phones will, the only alternative I can see if another replacement phone. Logic says, that if your phone will not work in your car but other people's phones will; and if your phone will not work in other people's cars but theirs will, the common denominator here is your phone. I would make another visit to Apple.
The only other thought I would have would have to do with your backup. If you are restoring the new phone from your backup, try to set up the new phone as a new phone and manually sync just your contacts to the phone. There may be something corrupt in the backup. After adding the contacts, test the phone. If it works, then sync the balance of your content. While you will lose saved app data and SMS history, as long as you have synced and imported photos, etc., you will have that backed up if needed and will be able to sync other content back