Apple announced OTA (Over-The-Air) iOS updates as part of the iOS 5 features to eliminate the need of a computer to update iPhone, iPad or iPod Touch Firmware. However, the keynote only mentioned the delta-style updates over WiFi networks only. Now, 9to5mac has discovered – through the iOS 5 SDK – the mention of over-the-air iOS upgradetes over 3G networks.
Based on these findings, it looks like only small point iOS updates like 5.1.1 (may be 5.1 as well) will come over 3G networks but bigger updates like iOS 5 / iOS 6 will come over WiFi networks only.
This update requires a Wi-Fi network connection to download.
Carrier support dependency is yet to be confirmed. Please note that Over-the-Air iOS updates will only begin if your iPhone has enough battery life and available storage (looks like Apple will expect 500 MB of necessary storage per delta update).
This update requires at least %i%% battery, and 500 MB of available storage.