iPhone - Get Position of UIView within entire UIWindow

That's an easy one:

[aView convertPoint:localPosition toView:nil];

... converts a point in local coordinate space to window coordinates. You can use this method to calculate a view's origin in window space like this:

[aView.superview convertPoint:aView.frame.origin toView:nil];

2014 Edit: Looking at the popularity of Matt__C's comment it seems reasonable to point out that the coordinates...

1. don't change when rotating the device.
2. always have their origin in the top left corner of the unrotated screen.
3. are window coordinates: The coordinate system ist defined by the bounds of the window. The screen's and device coordinate systems are different and should not be mixed up with window coordinates.

Swift 5+:

let globalPoint = aView.superview?.convert(aView.frame.origin, to: nil)

Swift 3, with extension:

extension UIView{
    var globalPoint :CGPoint? {
        return self.superview?.convert(self.frame.origin, to: nil)
    }

    var globalFrame :CGRect? {
        return self.superview?.convert(self.frame, to: nil)
    }
}

In Swift:

let globalPoint = aView.superview?.convertPoint(aView.frame.origin, toView: nil)

Here is a combination of the answer by @Mohsenasm and a comment from @Ghigo adopted to Swift

extension UIView {
    var globalFrame: CGRect? {
        let rootView = UIApplication.shared.keyWindow?.rootViewController?.view
        return self.superview?.convert(self.frame, to: rootView)
    }
}