MaskInput

mask.js

maskTelefone: function() {
      $( "#telefone" ).mask( "(99) 9999-9999?9" ).live('focusout', function (event) {
        var target, phone, element;

        target  = (event.currentTarget) ? event.currentTarget : event.srcElement;
        phone   = target.value.replace(/\D/g, '');

        element = $(target);
        element.unmask();

        if(phone.length > 10)
          element.mask("(99) 99999-999?9");
        else 
          element.mask("(99) 9999-9999?9");
      });
    }