When I dial numbers that have been disconnected, I do not get a reorder tone or message saying that the number has been disconnected. The phone immediately hangs up.
Issue the "voice call convert-discpi-to-prog" global configuration command, available in Cisco IOS Software Release 12.2(1). Doing this converts a DISCONNECT message with a progress indicator value of eight to a PROGRESS message with a progress indicator value of eight so that audio is cut through and the Cisco IP phone hears the disconnect tones or announcement from the PSTN.