Clarion said they are only allowed a certain amount of communication with Apple. They do not know how it will be handled at this time - either a bug fix from Apple or a firmware update for the Clarion unit.
You can fax Clarion at 310-327-1999. The more people complain, the more urgent it will be to fix.
In the meantime you can downgrade your iPhone to version 4.3.5 by following the instructions located here
http://iphoneblogr.com/2011/08/how-to-downgrade-from-ios5-to-4-3-5-or-4-2-10/
This will restore connectivity with the Clarion. Or you can take the phone to an AT&T or Apple store and have them downgrade it for you, but you MUST be sure you have a previous 4.x.x backup in iTunes. iTunes stores the last several backups. You cannot restore an iOS5 backup to an iOS 4.x.x iPhone.
After the restore is complete you will need to sync your unit with iTunes to get your data back.