Huh? You don't have to open any ports on your network unless you want to use the router as a SIP gateway for IP phones. (Even then it's just a handful of well-defined ports.) Phone goes into router, router does all the VoIP PBX things. The VoIP traffic never goes through your firewall, which I assume sits behind the router.Provider did make those settings available. Unfortunately they also publicly posted default logins for their devices, so chinese bots keep knocking on my firewall quite often. For the same reasons I would not like to open ports they use.
And why would the default login thing be a problem, unless that always remains active even after you've set a password manually (which would be super dumb)?