I have problem with my Bluetooth too. I have iPhone 4 wit iOS 5.1.1 and use some headsets from Plantronics 975, Jabra, Blade and have every time the same problem with any of them. The pairing procedure is going always very well, but when I switch off any of the headsets for longer tome, for example more than 1 hour and then switch on the headset again, the headset cannot be connected to the iPhone automatically, nevertheless that the Bluetooth is on in searching mode. Very occasionally I found out the following procedure which works:
Settings>General>Bluetooth Off>Bluetooth On> Tap on the device name to connect
and the connection is established.
It is but very bore to this every time when I sit in my car and s usual I am in a hurry. I tried different thinks like to delete the device and pair again or to reboot deeply the iPhone the nothing helps. Has anyone solution for this problem?