Edit in JSFiddle

function getCustomerSSNById(customerId){
    return $.post("/echo/json/", {
            json: JSON.stringify({firstName: "Jose", lastName: "Romaniello", ssn: "123456789"})
    }).pipe(function(p){
        return p.ssn;
    });
}

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

function getPersonAddressById(id){
    return getCustomerSSNById(id)
           .pipe(getPersonAddressBySSN);  
}


getPersonAddressById(123)
    .done(function(a){
        alert("The address is " + a); 
    });