In an email sent today Apple has advised iPhone developers that all applications submitted to the App Store for approval will be reviewed using iPhone OS 3.0. Apple also warned that applications must continue to work after iPhone OS 3.0 is in public release or they could face removal from the App Store.

All apps must be compatible with iPhone OS 3.0
Millions of iPhone and iPod touch customers will move to iPhone OS 3.0 this summer. Beginning today, all submissions to the App Store will be reviewed on the latest beta of iPhone OS 3.0. If your app submission is not compatible with iPhone OS 3.0, it will not be approved.

Existing apps in the App Store should already run on iPhone OS 3.0 without modification, but you should test your existing apps with iPhone OS 3.0 to ensure there are no compatibility issues. After iPhone OS 3.0 becomes available to customers, any app that is incompatible with iPhone OS 3.0 may be removed from the App Store.

iPhone OS 3.0 is the next version of the iPhone and iPod touch operating system which is due for release in the coming months. See this article for further information on iPhone OS 3.0.