AMI call is sent to voicemail if i hangup

I originate a call via AMI. So the extension rings, i pick up and the call is routed to the external partner. In case i hangup or the extension is not available etc. the call is sent to voicemail and connected to the external partner, which then hears the voicemail message. This is slightly awkward and anoying for the partner. If i disable voicemail, the call is not originated.

Is there any way to disable voicemail for AMI originated calls or a special context which disables voicemail?

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The calls are originated with this php function:

function originate()
	global $connection;
	global $parameters;

	fputs($connection, "Action: Originate\r\n");
	fputs($connection, "ActionID: " . $parameters["callid"] . "\r\n");
	fputs($connection, "Channel: local/" . $parameters["extension"] . "\r\n");
	fputs($connection, "Context: outbound-allroutes\r\n");
	fputs($connection, "Exten: " . $parameters["number"] . "\r\n");
	fputs($connection, "Priority: 1\r\n");
	fputs($connection, "Timeout: " . $parameters["timeout"] . "\r\n");
	fputs($connection, "CallerId: " . $parameters["callerid"] . " <" . $parameters["number"] . ">\r\n");
	fputs($connection, "Async: false\r\n\r\n");