Bluetooth connection problem

I have a 2006 Prius with the navigation system (package 7) and a Samsung A900 cell phone provided by Sprint. The problem I'm having is that the Bluetooth connection has to be manually established each time I start the car. It's as if the car has "forgotten" the phone. Once the connection is up and running, I can turn both the car and the phone off and restart them, and the connection will still be there (as long as the two are near each other). But if I leave the car and return, it's gone. I've tried seemingly everything: profiles have been deleted and re-established and the "Auto Connect" button has been turned on. My dealership has been of limited help; I took it in but didn't leave it, and because the connection doesn't conk out immediately, it appeared to work properly. The navigation system was recently replaced, and, because the Bluetooth worked flawlessly before I took it in, I suspect they might be related. Any ideas?