I just today was interfacing to one of these 4x4 keypad arrays for a small in-house test box we're making at work. I was handed the keypad and told to make it go. No problem, they're pretty straightforward to work with. But my immediate question was, "can't we get one with a calculator style number layout rather than a phone style layout?" and it seems to be the answer is basically no, unless you want to have one custom made. Pretty much all the stuff out there floating around is all phone layout. Why?? The pattern on the one in your project write up (which is a fun project, btw) seems the most common, and the same pattern as the one I've got. Along with the reverse number pattern, the '#' and '*' keys seems much less useful than a '.' and an 'enter' key would be in a lot of applications.