function add_extension(a){
	// add extension 'a' in extensions.conf 
	// add 'exten => a,1,Queue' to default
	var uri;
	var i=1;
	if($('novoicemail').checked){
		uri = build_action('append', 0, specialcontext ,'exten', a+','+i+',Set(__Queue=True)');
		i++;
	}
	uri += build_action('append', 0, specialcontext ,'exten', a+','+i+',Queue(${EXTEN})'); 
	makerequest('u','extensions.conf',uri, function(t){return true;} );
}