I‘m using VirtualRecorder to record my lesson during class. Good quality and can convert to mp3 too. Also it has a mic preamp which is useful on situations when you are far from the subject Get it from the market, it‘s free.
As for 2-way call recording, from my experience on linux, it must be supported in the kernel
On the Galaxy S2 forums you can find more info regarding the subject.
I dont think Nvidia will soon (if ever ) release such feature. They are late even on the ICS kernel 3.0*
Also for a Dev porting it means getting the APIs working and coding the right baseband driver.
Sent from my Optimus 2X using XDA App