FreeSWITCH can be used to conquer NAT by simply wedging it between devices. You can configure a local FreeSWITCH and register all of your phones to it, then register that instance of FreeSWITCH to the SIP provider on behalf of all of your phones, carving a hole right through the NAT and keeping everyone happy. Also, you can set up FreeSWITCH on a public IP somewhere on the Internet, then register all of your phones or local FreeSWITCH instances from multiple locations to that common server, so even if both locations are behind NAT, they can still make calls between sites without a problem.
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