Comcast terms:
> use or run dedicated, stand-alone equipment or servers from the Premises that provide network content or any other services to anyone outside of your Premises local area network (“Premises LAN”), also commonly referred to as public services or servers. Examples of prohibited equipment and servers include, but are not limited to, email, web hosting, file sharing, and proxy services and servers
Verizon terms:
> You also may not exceed the bandwidth usage limitations that Verizon may establish from time to time for the Service, or use the Service to host any type of server.
AT&T terms:
> using such account for the purpose of operating a server of any type;
Sources:
https://www.xfinity.com/corporate/customers/policies/highspe...
https://www.verizon.com/about/terms-conditions/verizon-onlin...