[UX] the default function for the history screen is dangerous
The default function (the big round button in the center) is almost always non-dangerous where it can't cause dataloss. The exception is the history tab where the button is a wipe of the history. I didn't recognize the icon and just pressed it, causing me to lose all my history.
I don't think this is the best choice of default button there.
My suggestion is to do what Android does; the default button selects the last number (top entry). Nothing more. As a result the screen will change and thus a second press will start dialing. Benefit is that you can use the same icon on both tabs.