Edit in JSFiddle

function getCustomer(customerId){
    var d = $.Deferred();
    $.post(
        "/echo/json/",
        {json: JSON.stringify({firstName: "Jose", lastName: "Romaniello", ssn: "123456789"}),
         delay: 4}
    ).done(function(p){
        d.resolve(p);
    }).fail(d.reject); 
    return d.promise();
}

function getPersonAddressBySSN(ssn){
    return $.post("/echo/json/", {
             json: JSON.stringify({
                            ssn: "123456789",
                            address: "Siempre Viva 12345, Springfield" }),
             delay: 2
    }).pipe(function(p){
        return p.address;
    });
}


function load(){
    $.blockUI({message: "Loading..."});
    var loadingCustomer = getCustomer(123)
                            .done(function(c){
                                $("span#firstName").html(c.firstName)
                            });

    var loadingAddress = getPersonAddressBySSN("123456789")
                            .done(function(address){
                                $("span#address").html(address)
                            });
    
    $.when(loadingCustomer, loadingAddress)
     .done($.unblockUI);
}

load();
<ul>
    <li>First name: <span id="firstName"></span></li>
    <li>Address: <span id="address"></span></li> 
<ul>
    

              

External resources loaded into this fiddle: