There’s a new modded Phone.apk available that will automatically record your calls if you are using a Samsung Galaxy S running Android 2.2.1 — note that it will probably not work on Android 2.2.
The Phone.apk is modified to automatically record both incoming and outgoing calls — of course it can be disabled — and save the conversations to the CallRecords folder on your SD Card, inside Sounds. There are a couple of settings which you can manually change — like the template system for flexible naming of recordings — but there’s also an Automatic Call Recording Control application that will make your work easy. For more information and details on how to flash the Phone.apk as well as revert to your original version, follow the source link to the MOD thread.
Warning: recording phone calls without the consent of both parties is illegal in some regions. Other regions only need one party to be aware of the recording in progress. Please make sure you know your legal rights and obligations before proceeding to recording phone calls!
Source: XDA Developers