Which SDK should you compile for? 2.2.1? 2.2? Choosing an active SDK version can affect both your target audience and possible App Store sales. We recently wrote about SDK choices, noting that building for 2.2.1 (the latest version, as of this writing) might cut out users who had yet to upgrade from the 2.2 firmware.

Ars readers responded both in comments and e-mail, asking whether delaying the firmware upgrades were typical of iPhone users or whether they indicated the relatively small audience of jailbreakers, who purposefully held off on upgrades. To answer this question, we turned to a few experts on the subject.

A developer posted on a Russian iPhone forum yesterday that upon receiving the latest beta iPhone software, version 2.2.1, he discovered the much-awaited presence of push notification support. Woo hoo! He describes OTA syncing of Apple’s notes and calendar apps and the presence of push notifications to indicate that new notes are available. While you may have read this news around the net this morning and gotten pretty excited, anticipating a day when software such as Instant Messengers and social networking apps might actually be useful on the iPhone, we thought it was important to let you know that today is not that day. The site that houses the forum has posted an update to the blog post that brought attention to the push notification claim, and has stated the original posting was indeed a fake. So iPhone owners, don’t do your happy dance just yet. Apple still hasn’t made good on its push notification promise and while it’s certainly possible that the iPhone may get support soon, it’s still looking unlikely for 2.2.1.