Free software to record phone calls

Hey everyone.
I have been looking on F-Droid but found nothing. I need a free software that allows to be installed in android (I am using CM7) to record phone calls. In my country companies can make a lot of deals over the phone, but later they change the rules of the contract and you can never request the original audio of the call (they keep one, but only present it when it suits them). So, I will start asking in the beginning of those calls "can I record it?" and if they say yes, I will record, if they say no, I will say "Contact me by letter, preferably a registered one".
Problem is, I can't find any way to do it. The standard audio recorder on CM will not record phone calls :(