I have an application that I would ideally like to run on all iOS versions, however I think Apple accepts apps only from a version and above (3.0 I think, but not sure). So my question would be, what's the minimum iOS target version you can send in review (and get accepted). If anyone with greater iOS publishing experience would answer my question it would be great and maybe point out some places where I can read about it.
Many thanks!
Sometime last year, an Apple DTS employee posted (and later clarified) on the iOS Developer Forums that the App store would no longer be accepting apps with a Deployment Target lower than 3.0. That might indicate that a lower Deployment Target has or will become grounds for an app to be rejected.
I would never set the Deployment Target lower than that of the lowest OS version among the devices I plan to use to test the app before submitting it to the App Store.
Also, the installed based of devices which haven't been upgraded to 3.0 or above might be too microscopic to be worth a developer's time or effort (unless you happen to still have and use one for some reason).
ADDED in 2013: App store submission now requires that the app support the 4" display, which requires iOS 6.0 or later, which allows a minimum deployment target no lower than iOS 4.3
You can only build your apps with the SDKs you have installed.
Since XCode will nuke your old SDKs whenever you upgrade (unless you install XCode elsewhere), it is assumed that you will always be building using the latest stable SDK version. This is in contrast to, say, Android, which will always retain SDKs whenever you upgrade.
Your deployment target can go back as far as you want, right back to 2.0 - but you may find it difficult to actually test it on that platform! Most people would just target 3.x upwards, which gives you as close to 100% coverage as makes no difference.
To back up what hotpaw2 indicated, this is from the News and Announcements for iOS Developers on June 29, 2010:
ok... strangely Im having a hard time verifying this... but it's my belief that you must build your app with the latest base SDK (4.0), but you can target an IOS version all the way back to 2.0. Ill continue to try to verify that.