iPhone App Version - which one to keep?

I just finished my first app developed in XCode 3.2.1 in iPhone Device 3.1.2. I know that there is iPhone 4 now, does that mean that I have to upgrade to iOS 4 before I submit my app to App Store? Or do I keep two versions of my app, one is the 3.1.2 version and the other iOS 4 to cover all iphone market (old an开发者_高级运维d the latest one)?

---

You should download and install the iOS 4.2 SDK.

You should then compile and link against the iOS 4.2 SDK.

It is likely that Apple will end support for 3.x in the near future.

Also, sort out your acceptance rate problem...