That's fine and good if all your customers are residing in the US or Canada.

If you succeeded with your formatting I (living in the Land of OZ) would have a problem creating an account with your store as all phone numbers in Australia are 10 digits including a 2-digit area code (except for some 13 numbers). Our mobile phones have a 4-digit prefix. Same would apply to people form other parts of the globe. Could result in a loss of orders for you.