Hi,
 We collect the CMR files and notice that all IP Phones seem to report 0 latency (that is when the CMR devicename=IP Phone).  When the CMR devicename is a gateway, voicemail port, etc, then latency can be > 0.    Jitter and MOS can fluctuate for IP Phones but latency I would expect to be > 0 ms, even on a LAN.  
 
Thanks