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In my experience, this is not the case and the only port that needs to be opened is 69.
To save excessive time configuring your modem and potentially creating unnecessary vulnerabilities, set your modem/router to forward port 69 to the IP address of your voice adaptor. Then try to re-configure your adaptor online as shown in your set-up processes.
It's worked for me for 2.5 years with both the Cisco ATA186 and also the current Voyager 10v.