This feature has now been implemented. There is no tally (number) of how many messages you sent as it was annoying. To view your sent messages, just click on the sent messages envelope and they will appear in order.
One thing you need to remember is...... If the person you sent the message too deletes it, it will NOT show up in your sent box.
Once received messages are deleted they are gone forever.
also, there is no way to delete sent messages from your box.
enjoy!