No because the OP is talking about saving a number that previously didn't exist on the phone and he doesn't already know so he mentioned the keypad sucks because you cant simply have the phone out, talking to someone, be able to just type in the number and have it keep it on the screen so that after the call he can save it for future reference.
WE ARE NOT talking about simply calling up someone, talking, hanging up and having the number in the recent call list to save. You encounter a situation where you call someone up a family member a friend and they say hey let me give you a number and usually you scramble for a pen or some way of to save the number? The OP was referring to the fact that you cant do it when you can but its kind of ass backwards.
You CAN save a number that didn't exist on the phone. I think text messaging or notes can do the job, because I'm sure you can click the home button and multitask while you are talking.