I've done all the hacks to get Bluetooth automatically reactivated after waking from sleep, etc., on 10.5.7 and a internal Broadcom (BCM92045) module I bought from HelloWifi on eBay. Hacked the Bluetooth plist to include the vendor and device ID to allow activation/deactivation, and added bluetooth activation to SleepWatcher.
But despite being able to set up iPhone tethering, I'm not finding it terribly reliable. For me, it's perfect via USB, but really flaky with Bluetooth. Bluetooth turns on when I want; I can pair; I can usually connect to the network; unfortunately, the serial connection always seems to drop after a few minutes. After a dropout incident, I'm often unable to reconnect, even after rebooting both devices. Any ideas?