Will the iphone 4 be able to get iOS 7?

I really need to know to buy it

Its Free And they will release it the 10th of september

Yes. With a few limitations (i.e, it will not have control center)

Yes, & the 4S, 5, 5S & 5C.

Expected on the 18th.

@Cristian: the 5S is being announced on the 10th, iOS 7 will not be released on that day.

Yes, it will. In fact, you can install it now if you register your device's UDID with a developer account through a site like http://www.udid.in/.It's $5, and then you can try out the new OS before everyone else. That's how I got it on my 4S.

Yes. Although a few features will not be in it due to age. I doubt the 4 will take any later versions since the 3GS will not take 7.