WCF: Cómo detectar la IP del cliente.

El código de ejemplo sería así:

OperationContext context = OperationContext.Current;
MessageProperties messageProperties = context.IncomingMessageProperties;
RemoteEndpointMessageProperty endpointProperty = messageProperties[RemoteEndpointMessageProperty.Name] as RemoteEndpointMessageProperty;

return string.Format("IP: {1}, Puerto: {2}", endpointProperty.Address, endpointProperty.Port);