Just to mention that if you use Pandion as your client, you can patch it as follows:
Use the files linked from the first post together with the code lower down in the thread. It works splendidly, with incoming call notifications, presence updates, and dialling. It also scores over Spark because it works on 64-bit processors, and can use Integrated Windows Authentication (aka Single Sign-On, SSO) with a Wildfire patch.
Hope this is of interest.