When using the sample code in the documentation:

$ec2_instance = new Zend_Service_Amazon_Ec2_Instance('aws_key',
                                                     'aws_secret_key');
$return = $ec2_instance->describe();

to return a list of instances, I got no results. But I was indeed running an instance. After searching I found the solution here: http://developer.amazonwebservices.com/connect/… . I successfully managed to list my european instances when changing the following:

const EC2_ENDPOINT = 'ec2.amazonaws.com';

to

const EC2_ENDPOINT = 'eu-west-1.ec2.amazonaws.com';

I suggest adding a setEndpoint / setRegion method to the Ec2 classes.