We have Cisco SPA504G IP Phones. Some of the phones work just fine, some others can call out but cannot hear the person called. The phones are plugged into the same network. If I take the phones to another location (residence) the phones work just fine. We have opened all the ports on the firewall required for the phones.
Can't figure out why some phones work and some don't. All phones are setup with Static IP's and are configured the same.
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