Prowl
A must-have $3 iPhone application that forwards Growl notifications from your Mac to your iPhone or iPod touch using Apple’s push notification service.
This could work in a pinch to get Twitter push notifications; just enable Growl in Tweetie (or Twitterrific) for Mac, and leave it open. When you get a DM or a mention and the Growl notification is triggered, it will be forwarded to the iPhone and you can then check the actual message on your favorite iPhone Twitter client.
