Hi Cipher,
You can use Odata to get Notes data for any entity.
Below is Odata url that will fetch the Notes Data.
http://Servername/orgname/xrmservices/2011/OrganizationData.svc/AnnotationSet?$select=AnnotationId,NoteText,Subject&$filter=ObjectId/Id eq guid'54994212-F683-E311-BB31-000C29E9425D'
Regards, Saad