Messi.im V1.40 was just approved by Apple, so it should be available in the App store soon:

• Video Messages: Send Video Messages from an iPhone 3GS. Videos can be saved and viewed on all iPhones/iPod Touches.
  We allow 2 quality settings either 15 Seconds High Quality or 30 Seconds Low Quality.
• ReadCheck: If this is enabled you can see if your friend has received your message.
• Custom Dialog colors and variable font size

Work on Messi.im V1.50 has already progressed quite far, it will have group messaging and some other enhancements.