Hi,
This is a pain to get working and I am having MAJOR issues with this at the moment. But the short answer to your question is...
Ensure port 2445 and 8443 are open across the network.
The phones do a certificate check against whats in their flash when you try and get a service list. If they have no certs then they download them from the CM on port 2445. It then does all kinds of comparisons to ensure authenticity and only once they pass this will it allow the services to be used.
No port 2445 = no certs = no services.
Browse to the ip phone and check the console logs on it after youve tried to get services. you may see the connection going out on 2445. post the results here and ill take a look and let you know what i think.