You can do a GET request against the Contacts Collection using the "status" and "modified_since" query parameters to filter the list. Modified_since limits the response only to Contacts who have been modified since the date provided, so it would not be only new Contacts but also Contacts which had been updated in the time range. You can find out more information about these query parameters here: http://developer.constantcontact.com/docs/contacts-api/contacts-collection.html
Dave Berard Senior Product Manager, Constant Contact
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