(via the Official Google Blog)
Google now offers a flight info service (for flights departing from or arriving in the U.S.) with information from flightstats.com.
Just text your flight number to 466453 (which spells google if your phone has a traditional key layout – on my blackjack I had to add this to contacts to remember it) and you’ll get an SMS with the status.
(Haven’t tried this yet as I’m in Switzerland this week, but I’ll try it later this week for my flights back)