Welcome to Android Central! Do you know where the voice recordings are saved? I believe it's in the /Sounds directory, but it might vary with the phone. Use a file manager app to copy that file to the Ringtones directory. As long as the file is mp3, wav, or ogg, it should be usable as a ringtone.
What message do you want to record? Your outgoing voicemail message? Go to your carrier's website and search for voicemail instructions.