I've recently upgraded my stereo in my truck to one that has bluetooth capability and can act as a speakerphone while I'm driving. I have been looking all over my phone and can't seem to figure out how to set up the right convenience key to turn on bluetooth without me having to go through a bunch of different menus. I'm trying to make as user friendly as possible so I will actually use it and I can justify to my wife the extra expense that I laid out for this stereo.
I would say both posts above me are good solutions, QuickLaunch is my favorite. You could also set the convenience key to "Manage Connections" That is only two clicks and a simple scroll to turn it on and off then.
leaving bt on is a battery consumer, i use shortcutme and love it (still finding things i can add shorcuts too). shortcutme has a free trial if you wanna give it a go.