The Registry is a mechanism through which loose coupling and location transparency can be achieved apart from EPR availability. The Registry default provided is based on jUDDI with different embedding strategies described in the programmers and services guide.
Integrations with other registries such as HP SOA Systinet do exist but lacking the embedded/local integration.
Through service binding other transports can also be registered [An example would be JMS]
Ideally, you should be using the ServiceInvoker abstraction and not having to deal directly with the registry