How do I disable update warnings on my iPhone?

I got a bought app (i.e. not a free one - be it given to me, bought by me or gifted, I don't know). It works great. Then some update for it comes along with many other updates for other apps. I press "update all" and every time this one app gives me a notification that I need to buy it because it's a new major version or whatever. Well, I don't want to do it, it works fine the way it is (probably because I was still in iOS 3.1.3)!

So, how can I just remove the future updates from the list? If there is any way to do it, that is.

^{P.S.: Now I upgraded to iOS 4, the app stopped working and I decided to just delete it along with another couple of apps which had a similar issue.}

You don't get charged for app upgrades on iOS. You only get notification for free updates.

It is possible you had run into whatever is described here (the comment 9:09AM on 3-05-2010 and further): http://www.tuaw.com/2010/03/04/paid-app-upgrades-coming-to-app-store/2#comments

So seems clear iPhone checks the installed apps vs iTunes store but when you click update all and it asks for the updated app, iTunes says "nuh-uh! you did not purchase this one, i am not signing/certifying bundle for you"