The Windows Mobile 5 Smartphone calculator looks (and is) awfully weak. However, while it is an “old skool” 4 function calculator, it is reasonably easy to use if you know its keypad shortcuts. The Smartphone’s navigation rose provides the four functions as well as the equal function. Press the top of the nav-pad for + (add), press down for – (subtract), left for / (divide), right for X (multiply) and the center for = (equal; complete the calculation).
The bottom-left key on the numeric keypad (labeled * T9) types in a decimal point (.) while the bottom-right key (labeled #) can be used for addition (+).
And, that is pretty much all the Microsoft provided calculator can do on the Smartphone. No square root, no trig functions, nothing. Very 1971 “old skool”.