Mistakes are unavoidable with any buttons on the screen, but in most cases they are harmless: you can just press back or close from the next view. However, calling is one of those activities that a) cost you money and b) annoy the other person if you call them by accident. So if there are cases that require you to tap again, in relation to calling features, some of them are done on purpose. Yes, you may or may not like them, that's fine.