The problem with recording is dependent on the kernel if that kernel has the capability to do so within the audio hardware driver!
That aside, another aspect, this governs actual phone calls, is that audio is a mutually exclusive thing, lift handset, audio, speaker is routed to respective hardware pieces, if not in call, audio and speaker gets routed to speaker (combine that with headset and another route is made!)
Now I do not know if that principle applies to VOIP over wifi (as have never tried it!)
Another thing, depending on where you are, this will be dependent on jurisdiction of your country, two way recording could be seen as illegal and may/could be equivalent to wire-tapping, IANAL!
Check first, if that's "ok to do", then check with the party involved first if they actually mind being recorded, if not, then you could end up in trouble for invasion of privacy and recording their conversation without their consent
I am loosely saying that as its a questionable thing to do and do not know legalese but its something to bear in mind.