08-26-2010, 01:01 AM
You could use something like the Twitter app Echofon (or similar). In addition to being a regular Twitter client it has a private messaging system (private in the sense it isn't broadcast like a regular tweet). I think it can be set for push notifications. It limits the number of characters that can be used like something like IM. It may or may not be free. If it's not, I may have paid (no more than) $2.99. It is free for all messages afterward, though.
Hope that helps. Good luck.
Hope that helps. Good luck.