Q931 decoders are not going to help here. The debug traces clearly show an outgoing setup, the far end rings for 8 seconds and then the call is cleared from the gateway.
This means there is nothing wrong with the ISDN side of things.
Most common reason you see 'resource unavailable, unspecified' clear code is due to a codec mismatch on H323, or a lack of dsp resources on the router for either normal call processing or transcoding/conferencing/mtp. Since this is under MGCP control, the codecs are specified under the CCM control so there should be no mismatch.
Therefore we need to see what is happening at the MGCP side of things. Make a single test call and obtain the log from 'debug mgcp packet' , then turn this debug off and get a log from 'debug voip ccapi inout' for a similar test call. Make sure you do this when only one call is up (the debugs are too hard to follow otherwise)
I experienced the same behavior once I exhausted all my DSP Resources on my 2800's that hosted my Pri Trunks at a previous company. The solution was to purchase more PVDM's and calculate my DSP requirements more accurately. I recommend using the Cisco DSP Calculator that can be found here.
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...