When I receive a call, I add it to my contact list. The contact program automatically assigns "home" as the label for the number being added.
I've never added a "home" number. 90%+ numbers are cell numbers. There is no feature that allows me to set the default label for a number added - at least that i've found after looking for a couple of hours.
Perhaps there is a hack to assign "cell" as the default label when creating a new contact from a number in the call log?