The nice folk at Apple don't want you to use bluetooth for their devices to communicate with each other as "We prefer Apple customers to use more secure methods"
Since the 3GS came out all iPhones are made so that only devices that match at least one of only 5 different BT profiles would be able to communicate with the iPhone. If you have any BT devices made before the 3GS then it is unlikely they will be recognised either.
Also depends what hot spot you want to connect too, e.g if it's a Bt one you have to be registered to use them to pay for it or be a btinternet customer...
Or If it's a pub or cafe you just need their password
LOL, one of those.
Personal Hotspot doesn't even use bluetooth when going from iOS to iOS.
Its all done via WIFI
Again with the greatest of respect, don't answer a question you either dont understand or dont know the answer to.