When I popped my SIM into my iPhone it forced me to download a configuration profile with a self-signed Vodafone cert, which means they can mitm any connection. I think this is required by the government so they can block adult websites by default? (I've also seen torrent websites also fail silently with misleading "server not found" errors)
I haven't looked into if they're doing the filtering via DNS or mitm, but I avoid the censorship by connecting to a vpn.
The filtering in the UK is by inspecting HTTP requests, so when a single image on wikipedia.org was blocked, every request to Wikipedia ended up going through each ISPs hidden proxy. [3]
According to [2], HTTPS sites aren't filtered -- but it references a page from 2004. I suspect HTTPS sites are now simply blocked outright at either DNS or IP level, but I don't have a way to verify this, and can't find any details.
[1] https://wiki.openrightsgroup.org/wiki/Internet_censorship
[3] https://en.wikipedia.org/wiki/Child_abuse_image_content_list...
[2] https://wiki.openrightsgroup.org/wiki/Cleanfeed#cite_note-LI...
Correct me if I'm wrong but I'm pretty sure this enables complete MITM by Vodafone when using cellular network.
http://imgur.com/b0il5xb http://imgur.com/3mw5ZGZ http://imgur.com/6ehhfuZ
The "server not found" errors sound like DNS blocking, which they can do without MITM.