Is an iPhone call recorder theoretically possible? NOTE: I know neither the iPhone SDK or Objective C, just wondering if possible.

I know obviously it would have to be on a Jailbroken device anyway, but it is technically possible for a iPhone call recording application to be made, or is it not possible to hook into the calls or the audio input/output?

I know obviously there would be no 'official' way of doing it and certainly not from an App Store application. And I know there are call recording apps which place outgoing calls through their own servers.

Just wondering if the reason it doesn't exist yet is just because no-one has coded it or if it's not actually possible?
On Jailbroken iPhones, SpoofApp does call recording. I am not a laywer, but note that recording calls may not be legal depending on where you are and/or where the other party is.