"I still think network level ad blocking is a terrible idea though, and I'm still kind of expecting some legal or regulatory move to put the kibosh on the whole idea."
ACK, since it 'breaks the internet' and violates any concept of 'net neutrality'.
a simple client-based program or web browser plugin is a better idea. phone providers could even pre-install them. MITM-based filtering works for corporate firewalls, but doing that for wide release again "breaks the internet". It's a pandora's box we don't need opened.