Bruno Renié has written a nifty app:iPhone push notifications for Twitter with Prowl
With the power of Prowl it pushes a notification to your iPhone when someone mentions you on Twitter. You first need to install the Prowl app on your iPhone and then go to their website to get your notification key. Then, go to Bruno's site, sign in with your Twitter account (OAuth, so no password give-away) and badabing! you get instant notifications on your phone, for free, when someone mentions you.
If you're one of those people who use Twitter instead of instant messaging and have lots of mentions this might be excessive for you but if not it can be very useful if you are like me who is very slow to spot that someone has replied or mentioned your name.
Great work Bruno!
This is particularly handy with the command-line growlnotify utility - I've used it a lot recently to let me know when long uploads finish without having to hang around watching them.