This seems to be a known bug CSCdw50476 on the CCO . The Display information element is not understood by the Call Manager properly. Hence, the ISDN call fails. The earlier Cisco IOS versions on the gateways like AS5300 had this problem .It has been resolved in version 12-2.8.5T, 12-2.6e and later ones.
For confirmation, you can verify all the configurations on the ITS 2.1 from the documents given below.
I'm not able to access my old voice mail messages all of a sudden. The recording says something like 'the message is currently not available'. This has never happened before in all the years I have been using this system. I have t...