When I had Verizon DSL, it was in the TOS that servers not be run on your line. There was nothing they did to stop it though. We have Verizon Business DSL at the office and anything goes there.

I remember having an issue with one of my ISPs about running something over port 80. I think it was Verizon DSL. I really can't remember though. That was just plain stupid because almost anyone savvy enough to run a webserver at home can figure out how to make it listen on another port.

My parents have Optimum Online and you can only use optonline.net to send outgoing mail. Any other traffic on port 25 just hangs there. That's not horrible, but I don't like it.