Solução Mask input para Telefone com 8 e 9 dígitos

mask.js

// jQuery Masked Input
$('#celular').mask("(99) 9999-9999?9").ready(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");  
    }
});

/*
 Quem encontrar problemas com o "target", utilize esta alternativa
 Enviado por: Irineu <irineujunior@gmail.com>
*/

$('#celular').focusout(function(){
    var phone, element;
    element = $(this);
    element.unmask();
    phone = element.val().replace(/\D/g, '');
    if(phone.length > 10) {
        element.mask("(99) 99999-999?9");
    } else {
        element.mask("(99) 9999-9999?9");
    }
}).trigger('focusout');