In case you were not aware, most answering machines have a record feature that allows you to record your phone conversation.
Any interesting article about recording phone conversations and its use in court can be found at:
http://yarchive.net/phone/call_recording.html
From this article, it seems that it is legal to record a conversation (without telling someone...journalists do this sometimes), but it's not direct evidence in court, but could be admissable to corroborate testimony.
The guy presents an interesting tip to help prove authenticity:
"One of the big things you'll need to do is to be able to prove the authenticity of the tapes and to prove the time and dates of the recordings. What I did was after the call was finished and with the tape still rolling, I'd dial the local time and temp. number and get a time stamp or for really important calls, I'd call the National Observatory number in DC. The DTMF would be recorded and the charge would show up on the phone bill."
Here's the number: 202-762-1401 (
http://tycho.usno.navy.mil/)
I just called it myself and it works.
Fight the Patent!