Samsung Galaxy S II :: Cancelling The Default Selection?

I ticked a "remember this choice" for texting to one of my contacts that has more than one mobile number, so it became the default. I didnt realise that the choice also applied to phone calls. No problem I thought, just unmark it as default. But that doesnt seem to be an option, i.e. having set a default, the only choice seems to be to change it to another number not actually cancel altogether.The only way round it i could find is to add a new dummy number, mark that as the default then delete the number. Am I missing the obvious?