Swordmaker, any idea how an out of service iPhone linked as a security camera through an iOS approved app fairs in this regard? Should I dig out my AirPort Extreme to replace my U-verse router? Sounds like this is on a whole other level of authentication for that to make a difference.
As to the iPhone, security would depend on the model and how old it is. Anything capable of running iOS 8 and better on an iPhone 5s or above I think would be good. At my office we eschew using the Comcast provided WIFI router except for the free patient use, and use a locked down Apple AirPort Extreme for its security connected via Ethernet to the Comcast router and lock that connection down.
With those caveats, it could work fine.
What screwed up our office phones waltzed right through the Comcast firewall and into the Ethernet connected phone system. It probably would not have made it through our AirPort Extreme firewall and onto its Ethernet network. . . nothing downstream on that LAN was effected.