There's no magic/instant solution. The issue needs to be analyzed first. Turn on syslog&debug messages (highest level) of Voice application and record them. Once issue will manifest the messages may help us to identify the cause.
Also, state of frozen ATA needs to be discovered in more details than just 'www is down'. Is it possible to ping the device ? Have it Ethernet link ?
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Well, I can try blind shot. Have you those devices located in public network (e.g. reachable from public internet) ? Then we can be almost sure we know the cause. You need to firewall them carefully.
