iPad, the new tablet-form computing device from Apple, is running on iPhone OS 3.2, which is higher version than the iPhone OS software that runs on iPhone mobile phone. While the iPad is shipped with iPhone (or iPad) OS version 3.2 built-in, Apple nonetheless still releasing iPhone OS 3.2 with its SDK Gold Master (GM), mainly for developers.
With the release of iPhone SDK 3.2 GM Seed, all iPad apps submitted to the App Store must be built using 3.2 release. Developers enrolled in the iPhone Developer Individual or Company Standard or Enterprise Program can access the SDK and OS software of iPhone OS 3.2 for iPad by logging into Apple Developer Connection on iPhone Dev Center.
Note that the end-user license agreement for iPhone OS 3.2 has been changed to indicate the privilege of free upgrade for iPad devices:
Apple will provide you any iPad OS software updates that it may release from time to time, up to and including the next major iPad OS software release following the version of iPad OS software that originally shipped from Apple on your iPad, for free. For example, if your iPad originally shipped with iPad 3.x software, Apple would provide you with any iPad OS software updates it might release up to and including the iPad 4.x software release. Such updates and releases may not necessarily include all of the new software features that Apple releases for newer iPad models.
In other words, customers who buy iPads now will likely to have to pay to upgrade to iPhone OS 5.x or later releases.
Direct Download Link for iPhone (iPad) OS 3.2
iPad1,1_3.2_7B367_Restore.ipsw (457 MB)
Direct Download Link for iOS 3.2.2 for iPad
Update: iOS 4 for iPhone and iPod touch