By default, Bitcoin clients connect to other bitcoin nodes on TCP port 8333. If a user wants their Bitcoin client to connect to other nodes, they will need to allow outgoing TCP connections on port 8333, and also will need to have the ability to accept connections on that same port.
After spending an entire day effortlessly trying to get a bitcoin client working from a home computer, one ATT Uverse customer called customer support.
After hours of phone calls and messaging ATT finally told me the truth of what was going on, and only because I noticed it myself and demanded an answer. The internet is being routed through a DVR/cable box, and they confirmed the DVR also has a firewall.
ATT Uverse is a bundled package similar to what many of the other nationally known Cable Companies / ISPs are offering. Home Internet service along with your TV channels in one, with added benefits such as DVRs, streaming music, games, and much more.