Android
In Android, the virtual keyboard can be dismissed with the back button.
iOS
In iOS, the convention is to create an invisible button that fills the screen, set it to custom, and send it to the back (Layout --> Sent to back) and connect it to an action that releases all of the possible first responders as in:
-(IBAction) hideKeyboard:(id)sender {
[textField1 resignFirstResponder];
[label1 resignFirstResponder];
[button1 resignFirstResponder];
}
If you are using a Scroll View, you need to drop the UIButton onto the scrolling view. It is also possible to have the return button call hideKeyboard from a one line text field by selecting the event "Did End on Exit" and connecting it to the File's Owner icon as hideKeyboard.