Zfone in stand-alone form and the Google Desktop hard drive search-indexing engine are completely incompatible. If you have both, you'll find that zfoned isn't running if you do a process check:
If you need to run Zfone, shut down Google Desktop and start the zfoned daemon manually:
# /etc/init.d/zfone restart
Then choose Start > Internet > VoIP Encryption (or Zfone, depending on your specific menu setup) and restart Zfone.
You can find error messages in these log files:
/var/log/zfone_all.log /var/log/zfone_errors.log /var/log/zfone_tmp.log