There have been many posts on iPhone issues and there is a PDIM firmware update - see this thread
http://www.camaro5.com/forums/showth...ht=iPod&page=4
I have a first gen iPhone as well but have not experienced your issue - I have lost connectivity after turning the car off and returning - needing to reboot to have the iPhone recognized again.
Try a search to see if others have the same issue.