iphone - upgrading an application... what happens to customers?

I have an application that supports iOS 2.x.

I am about to revamp this app, but I need to make it at least 3.x.

What will happen to old customers? I mean, suppose a guy is using an old 2.x device and I release a 3.x app. Will this guy receive an alert on his iphone that a update is available?

I know th开发者_开发百科at iTunes is blind and allows one to download and buy anything, even if you don't have any iphone or iPad. Is that same guy be able to download the newest version even if it is not compatible with his iphone? and what happens to the old version? I mean, once the newest version is downloaded by itunes, it will overwrite the old version that iTunes was storing. So, when the guy tries to sync, not only he will lose the version he had, but also will not be able to upload the new one to his device.

I don't know if this line of thinking is correct.

Do you guys have experience with this?

Please tell me what happens.

thanks.

The person will get an error along the lines of "This app is not supported on your device" if they try to download/install it.

Edit: not sure what happens if they try it on iTunes though.

Itunes won't warn you as it doesn't know what OS you iDevice has. But there will basically noone on less than OS3