$(document).ready(function () {
    var areaCode = $('input.areacode'),
        exchange = $('input.exchange'),
        lastFour = $('input.lastfour'),
        body = $('textarea[name$="body"]');
    
    areaCode.bind('keyup', function (event) {
        if ($(event.target).val().length == 3) { exchange.focus(); }
    });
    
    exchange.bind('keyup', function (event) {
        if ($(event.target).val().length == 3) { lastFour.focus(); }
    });
    
    lastFour.bind('keyup', function (event) {
        if ($(event.target).val().length == 4) { body.focus(); }
    });
    
});