AT&T Blocked?

I’ve tried to access a site hosted at Dreamhost ( from both an AT&T cable modem and the AT&T cell network. Both were unable to access the site. My AT&T iPhone showed the following error:

Response Error.

Technical description:
502 Bad Gateway - Response Error, a bad response was received from another proxy server or the destination origin server.

Any ideas why AT&T customers would be blocked from accessing a Dreamhost site?