When using Topic/Subscriptions with the WCF publish/subscribe service model, for adding the service endpoint you must specify the topic URI (namespace/topicname) as the address, and the subscription URI (namespace/topicname/Subscriptions/subname) as the listening URI.
There are some samples that cover this scenario so may also want to cross check: 1) http://code.msdn.microsoft.com/windowsazure/WCF-with-Service-Bus-d3987eaf 2) http://code.msdn.microsoft.com/windowsazure/Service-Bus-netMessagingBin-9ae8ad13 3) http://code.msdn.microsoft.com/windowsazure/Brokered-Messaging-WCF-ed259f73