Some suggestions....

How about having a "Connecting" or "Attempting to Log in" notification popup in the upper right corner that pops up letting the user know what is happening. Also, once a login is successful, another popup saying so. Perhaps also, make the dial buttons, etc. grayed out until the login is successful so that users don't attempt to dial or do other things that obviously won't work unless logged in.

One other thing I noticed is that once I login, I can't view my GC contacts until (on the Contacts tab) I select 'None' in the dropdown combo and then re-select 'GrandCentral'.

Keep up the good work!