nested-deferred.js

function (number, country) {
  var req, valid = $.Deferred();

  req = $.ajax({
    type  : 'GET',
    url   : '/api/v3/validation-url',
    dataType : 'json',
    data  : {
      phonenumber : number,
      countryid   : country
    }
  });

  req.then(function (data) {
    if(data.valid) {
      valid.resolve(data);
    } else {
      valid.reject(data);
    }
  });

  return valid;
};

function (number, country) {
  var dfd = $.Deferred();
  
  $.getJSON('/api/v3/validation-url', {
    phonenumber : number,
    countryid   : country
  }).then(function (data) {
      if(data.valid) {
        dfd.resolve(data);
      } else {
        dfd.reject(data);
      }
    }, dfd.reject.apply(arguments)
  );
  
  return dfd;
}