After upgrading our CUCM cluster to 8.5 (from 7.1) we noticed that some model phones lost access to the corporate directory. When pressing the button they would get the error “Host not found” on the screen. After some trial and error we found that this was related to the firmware used on each phone. For example, a 7970 would work fine with firware but when upgraded to SCCP70.9-3-1SR2-1S the host not found error would creep up.
It turns out that Cisco has introduced a new set of secure URLs for phones to access CallManager over https.