My iPhone is NOT jailbroken, but I have been considering doing a temporary jailbreak until the SDK. Is there a way to unjailbreak the iPhone when the SDK is released?
You came to wrong place to ask this question, you really did, yes there is a way for you to do it, google around, and you'll find all the info you need.
You should be able to restore your iPhone - installing the current firmware version with no problems.
Some say Apple has no way of knowing but some claim Apple was able to tell when their iPhone was sent to AppleCare for testing and inspection. If Apple has a way of determining this, you risk voiding the warranty - if your iPhone is sent to AppleCare for a warranty claim.