Having the same problem on CME 10.0 + firmware 9-3-1.
Under telephony-service, I have following two lines,
hunt-group logout HLog
then in ephone-dn, added ephone-hunt login
The HLog key is grey-out. dialed by *3 didn't work either. Same config on CME8.8+F/W 9-2-3 works fine.
Took out the hunt-group logout HLog under telephony-service, the key appeared as normal but didn't do anything when pressed on it.
Not sure this is firmware issue? But the new phone has to use 9-3-1 or above.