"It's definitely something we want to do," Birdfeed developer Buzz Andersen told me in an e-mail. "Especially since we have an emphasis on notifications as a feature within the app." Andersen says they're exploring a number of possible long-term solutions.

Twitterrific developer Craig Hockenberry also said in an e-mail that he's working on push notifications, but wouldn't give further details at present.

In the short term, however, a sort of gray market for Twitter notifications seems to have--if you'll excuse the turn of phrase--popped up, with a few apps existing specifically to bridge that gap by pushing notifications to the iPhone and then allowing you to view the relevant messages in your favorite Twitter app--well, mostly if your favorite Twitter app is Tweetie or Twitterrific, anyway.

Both Polar Bear Farm's and appremix's take this approach--though Boxcar only lets you view mentions in a separate app. Both let you choose whether you want notifications for direct messages, mentions, or both.

Polar Bear Farm has in fact managed to turn this into a business model. Not only does the Tweet Push application cost $1 from the App Store, but you have to pay a monthly fee of $1 (one month's worth of notifications comes with purchase, free of charge). This is largely to offset the overhead of relaying the notifications, which is an ongoing cost for the company.