In an iDevice first, the latest development release of iOS (iPhone OS 5 Beta 4) is being pushed to developers wirelessly by Apple. OTA (over the air) updates are certainly not new: Android, Blackberry and WP7 users all currently enjoy this convenience. However, this is the first OTA update provided by Apple since they first enabled the feature in iOS 5 Beta 2 nearly a month ago.
The new feature will send iOS updates via both cellular data network (3G) and Wi-Fi (802.11x) to Apple's entire mobile line-up, including the iPhone 3GS (or newer), iPad (or newer) and iPod Touch (third generation and up). Updates beamed out to devices through cellular wireless are said to be delta patches only. Delta patches are updates containing only the differences between versions, thereby creating smaller path files and conserving bandwidth. As a result, users downloading updates through 3G are expected to be limited to incremental updates only (eg. iOS 5.0 to 5.1, but not to 5.0 to 5.3). Users who connect to their own wireless at home or in the office will receive the full updates OTA from Apple.
Currently, there are developer reports suggesting devices are not being updated properly without manually checking for software updates first. You can find this setting under Settings > General > Software Updates. Meanwhile, developers who have problems with OTA updates can still play with the new "iTunes Sync" feature which allows for wireless synchronization with iTunes.
The final version of iOS 5 is expected to drop this fall and brings a plethora of new features to iPhones, iPads and iPod Touches. You can find a thorough list of changes and features for iOS 5 Beta 4 here.