If I wanted to get, say, usage data about 'calls-inbound' AND 'sms-inbound', you'd think you could just pass an array in as the category param like so.
$records = $client->usage->records->read(
array(
"category" => array("calls-inbound","sms-inbound")
"startDate" => "2012-09-01",
"endDate" => "2012-09-30"
)
);
But this only returns data on the first array item "calls-inbound". Any way to get data about more than one category but not all categories?