Apple has released iPhone OS 2.2.1, a minor update to the device's firmware and operating system. Apple's release notes state only that the update increases the stability of Safari and resolves a problem in which images saved from Mail do not display correctly in the camera roll. However, users are beginning to discover several undocumented enhancements.
In particular, the update appears to address ain which users suddenly experience inability to send SMS text messages on the iPhone 3G, receiving the message "error sending" upon attempting to send.
Still unresolved, however, is a minor issue in which Google Maps shows incorrect units of measurement in certain countries.
In order to apply this update, click the "Check for Update" button in the Summary tab of the iPhone device pane in iTunes (with your iPhone connected).
Watch for further details on undocumented enhancements. If you've noticed a new feature or fix, let us know.
UPDATE: For iPod touch users, this update also issue that caused some Apple Lossless (ALAC) audio files to skip during playback
UPDATE #2: Problems installing Some users are unable to apply the iPhone OS 2.2.1 update at all, with the installation process failing partway through. In some cases, the phone may become stuck in recovery mode, typified by the image of a USB cable pointing at an iTunes logo.
If you are experiencing a similar issue, first try the steps detailed in this knowledge base article.
If you are using a Windows sytem, try completey uninstalling then reinstalling iTunes, as described in this knowledge base article.