Jade Ltd, is going to begin selling a product called My Logger. This thing plugs into the standard telephone and then into a PC via USB and will record your phone conversations to hard disk. It also has a built in microphone for tagging all your phone sex romps with voice memos. This product is available in Japan only right now for 35,700 (approximately $300 USD) and there is no word on whether it will come stateside.
My Logger [AkibaLive]
