I am also having issues with X-lite 5 not responding when dialing outgoing calls or receiving incoming calls, as I get voicemail notifications from calls that I did not hear ring. It works for a little while, but after about 10 calls incoming and outgoing, it stalls when calling out and stops receiving incoming calls. When I restart the computer, it is back to normal.
It worked fine before the upgrade to X-Lite 5. I am using Mac OS X 10.7.4.