I'm currently looking into creating a view for this within the application where you currently send messages.
If this is really important to you, you might try using TwitterBerry and disabling bbtweet at night. This way you get the benefit of instant delivery with bbtweet while carrying the device but can keep messages delivered while not carrying out of your inbox and just re-enable the next time you pick up the device. I'm currently doing this using a desktop client (tweetdeck or twhurl) to catch up on the overnight messages.
Again, I eventually plan to incorporate this in to bbtweet. It wasn't done from the beginning because that functionality already exists with TwitterBerry.
@jasmas
Sent from my Verizon Wireless BlackBerry