This! I once took over programming a point of sale system that our (internal to the company) users were complaining about. Turns out there was no concept of tab sequence, you had to use the mouse for everything. I asked the previous programmer to show me how to use the form he created, and he started typing a phone number using the top row of the keyboard instead of the numpad. But hey, it had lots of javascript!
I don't get your point about typing phone numbers. When I was being taught to touch-type in first and second grade, my teachers told me that I should type on the top row, not the numeric keypad. Not sure why. Maybe because it takes less time to move to the top row and back? Anyway, to me, typing numbers on the top row is not an obvious problem.
Presumably this is it. I find typing on numpad is much faster and simpler, but 1) laptops typically don't have one and 2) on normal keyboards it takes my hands away from the main keyboard. Then I switched to a Kinesis Advantage2 and now the numpad is integrated into the main keyboard, using a foot pedal to toggle between main keys and integrated keys.