We have some ShoreTel phones kicking about the office. We couldn’t figure out why they weren’t keeping time.
The reason was that the phones weren’t getting the SNTP time servers from our dhcpd server. I added:
option ntp-servers x.x.x.x, y.y.y.y, z.z.z.z;
… into the dhcpd.conf file and restarted the daemon.