iOS 4.2.1 Features
The main set of iOS 4.2.1 features that were released were not actually as relevant to the iPhone, as they were ensuring that the rest of the devices in the network were able to receive the main feature components for the iOS 4.2 update. For many people, this will simply act as the iOS 4.2 update if they did not get it before.
In general, the iOS 4.2.1 features are somewhat marginal and based around fixing small issues. There were occasional iPhone Wi-Fi issues that came up with the release of the iOS 4.2 update, as well as problems with music skipping when used with a car stereo. Voice Over iP problems had persisted for users with iOS 4.2 as well, and the iOS 4.2.1 update includes patches to repair these issues.
One major feature that may appeal to many iPhone users is that the Find My iPhone feature, that usually costs money with a MobileMe account, has become free for users with the iOS 4.2.1 update. This feature allows for users to utilize the iPhone's GPS features remotely, to find it if it has been lost or stolen, even locking the iPhone or having it emit a loud sound to make it easier to locate. It is only free, however, for iPhone 4, iPod Touch 4, and iPad users. This does not include iPhone 3GS and older models. Along with this, the Voice Memo application that comes standard on the iPhone, has a new icon image to add a new appearance.
On a special note, you will find that this will be the last iOS update for the first generation of iPhones. This means that iPhone owners up through the iPhone 3G will have to purchase newer models if they intend to remain current on the software.