Version #1 use a simple array
$collection = Mage::getModel('catalog/product')->getCollection();
$collection->addAttributeToFilter('sku', array('n2610','bb8100'));
$items = $collection->getItems();
echo count($collection);
Version #2 use a more specific array
$collection = Mage::getModel('catalog/product')->getCollection();
$collection->addAttributeToFilter(
array(
array('attribute'=>'sku','eq'=>"n2610"),
array('attribute'=>'sku','eq'=>"bb8100")
));
$items = $collection->getItems();
echo count($collection);