Universal method to record calls via Bluetooth in OS X 10.6?
Returning to this question several years later, it's still a pretty sad state of affairs. The only reliable answer is some sort of hardware solution.
In practice, this is what I ended up buying:
http://www.amazon.co.uk/Olympus-TP-8-Telephone-Pick-Microphone/dp/B007OXMHDE/ref=sr_1_11?ie=UTF8&qid=1400147804&sr=8-11&keywords=voice+recorder+microphone
It works really well; you connect the jack to a voice recorder and put the earbud in your ear, which has a microphone and sits between your ear and the phone's speaker. The quality isn't bad (albeit not broadcast quality) and the ability to use an external voice recorder means I'm not having to deal with moving files off my phone or expend extra battery power on a recording app.
That said, this looks really interesting (Though I'm unsure whether you just connect it to your phone and use normally, or whether you connect some sort of hands-free headset to the other side):
http://thenextweb.com/gadgets/2014/05/12/15-quirky-gadgets-accessories-buy-today-2/2/
Considering the question is ultimately about finding a cheap or free software-based recording solution, I'll leave it open in case anyone comes up with something workable.
Audio Hijack grabs audio at the OS level—anything coming out of the speakers has to go through the OS at one point or another—so I'm surprised AH can't grab the audio of those apps, but maybe it's a Quicktime thing that those apps are bypassing. Maybe give AH's devs a shout and see if they know a trick that will work. But, enough nerd talk...
If Audio Hijack can't do it, then I would go with a hard hack. Griffin has a cable that can redirect a call to external speakers and has a microphone to speak into. You should be able to output the receiving caller's audio to speakers and then capture that and your voice with your laptop's microphone. It will take some futzing with speaker placement to get the mix right, but it should work.
None of this is nearly as clever or convenient as hands-free Bluetooth, but that whole notion seems pretty well shot down anyway.