We have had an issue occur where external calls would drop or if picked up, would not return audio. It began sporadically and began to happen within an hour to most all of the IP Phones. I used sniffer to track one call which indicated that the call was going to the gateway but not being returned. After recycling the voice gateway, all external phone calls resumed normally. Any ideas on what caused this issue? And if so, is it the callmanager or the voice gateway with the problem.