AT&T Uverse does not block port 443 but…their wireless STB uses that port
I fought for days trying to get my Owncloud server to allow remote https access. At first I thought it was either my Apache 2 configuration or my DMZ Shorewall router (on a Debian Squeeze Pogoplug). I turned out that my wireless set top box was using port 443. That meant I needed to use a different port for my remote https access to Owncloud. I decided to route port 4430 on my router to port 443 on my Owncloud server (running Ubuntu 12.04). Worked great…so far.