PHP - убрать дубли в массиве по 3 ключам

Array ( 
[0] => Array ( [msisdn] => 79112221122 [called] => 7234346383 [dates] => 2018050108 [duration] => 13 ) 
[1] => Array ( [msisdn] => 79112221122 [called] => 7234346383 [dates] => 2018050108 [duration] => 12 )
) 

$used = [];
$output = array_filter($input, function ($value) use(&$used){
    $key = $value['msisdn'].$value['called'].$value['dates'];
    if(isset($used[$key])) return false;
    return $used[$key] = true;
});

Можно, сначала посчитать хэш для необходимых полей, а потом по их индексам сделать выборку из начального массива

$test = [
    ["msisdn"   => 1,
     "called"   => 2,
     "dates"    => 3,
     "duration" => 13,
    ],
    ["msisdn"   => 1,
     "called"   => 2,
     "dates"    => 3,
     "duration" => 12,
    ],
    ["msisdn"   => 1,
     "called"   => 0,
     "dates"    => 3,
     "duration" => 12,
    ],
  ];
  $test_array = [];
  foreach ($test as $key => $test_item) {
    $test_array[$key] = hash(
      'tiger192,3',
      $test_item['msisdn'].$test_item['called'].$test_item['dates']);
  }
  $result_index = array_unique($test_array);
  $result_array = [];
  foreach ($result_index as $result_key => $result_item) {
    echo $result_key . "<br>";
    $result_array[$result_key] = $test[$result_key];
  }

  echo "<pre>";
  print_r($result_array);
  echo "</pre>";

function unique_multidim_array($array, $key) { 
    $temp_array = array(); 
    $i = 0; 
    $key_array = array(); 
    foreach($array as $val) { 
        if (!in_array($val[$key], $key_array)) { 
            $key_array[$i] = $val[$key]; 
            $temp_array[$i] = $val; 
        } 
        $i++; 
    } 
    return $temp_array; 
}