Jott Assistant is in the same category as Voice Assist. You dial a number and start telling the Jott computer what you want to do. Jott's catch is that it only lets you send texts and e-mails; you can't listen to incoming messages. However, Jott does let you leave posts on an unrivaled variety of websites, including Facebook, Twitter, Live Journal, Google and Outlook calendars, Amazon.com, and Quickbooks. It also acts as a dictation machine to record your thoughts, and plays RSS news feeds.
For $4 per month you can leave messages up to 15 seconds. The $13 monthly plans lets you leave 30-second messages.