Much like audioblog.com's moblog feature, with AudioMail the user calls into a phone number (Vancouver only right now) in types in their account number. The user can then record up to a 5 minute clip.
Today AudioMail looks more like a marketing tool for the parent company Clipstream, the record time is too short and the service is not very useful for bloggers. When the recording ends the system sends you the link for your encoded clip. Us bloggers need a media file to point to e.g. MP3, MP4, etc. so our enclosures will pick it up and aggregators will fetch it.
With Audioblog.com you can either produce your media using their tools or upload your own, it costs $5/month. At this point I would have to say that audioblog.com is a better bet.