Saturday is iPad day, that much is certain, but there are rumors that the iPhone might itself get a little attention from Cupertino. Apple on Monday seeded the Golden Master--a copy of the final production version--of iPhone OS 3.2 for download to developers. It's part of the iPad SDK (software development kit), and for now will run only on the iPad. That means come Saturday, the iPad should be running iPhone OS 3.2, while the iPhone itself is still, as of this writing, is currently running 3.1.3.
Now that 3.2 is ready for prime time on the iPad, there's a possibility that it's ready for the iPhone as well. Apple, if it so decides, could release the Kraken that is 3.2 for the iPhone on Saturday alongside the iPad, giving parity to the two devices.
Generally, when Apple releases an OS update for the iPhone, a similar update is available for the iPod Touch the same day. This makes it easier on developers and users: an app that "works with 3.2" is easier to deal with than one that "works on iPad 3.2, iPhone 3.1.4, iPod Touch 3.1.3" and so on.
That being said, the iPhone family of devices has had disparity before. The iPhone, for example, for a time had OS 3.0.1 as the current OS while the iPod Touch was still on 2.2.1. Then the 3rd generation iPod Touch launched with 3.1.1 and, the same day, 3.1.1 was released for the iPhone to bring devices back into parity. But during that brief time (about three months) the two lines of devices were not using the same version of the OS--something that might happen again this weekend if Apple has decided that 3.2 isn't ready for the iPhone and iPod Touch.