Does anyone know why you're posting in this thread, that's over 10 months old? This is the Rumors forum, for discussing possible new products. Please post your question in the right forum.
From the messages screen, hit Alt+O to view sent items. Scroll up and click on the most recent date and select 'delete prior'. I think this will do what you're looking for.
Look at the icons to the left of each message in your Messages List.
items with a tick are your sent messages.
If you delete any of these from your message list and you have your sent folder synchronising with the handset.
Your sent items will also be deleted from the mail clients sent items folder.