(replying to myself is probably bad form, but I had another thought to note here) Most likely, the WiFi provided by carriers like AT&T is meant for offloading.

(replying to myself is probably bad form, but I had another thought to note here) Most likely, the WiFi provided by carriers like AT&T is meant for offloading. The phones will do EAP-SIM or some other authentication the customer has no idea of. That will get the voice and SMS traffic passing via WiFi and associated backhaul to the Mobile Core, instead of the mobile network. Assuming that scenario, where WiFi is really a low-cost extension of the mobile network, the carrier has very little incentive to do the "right thing" when it comes to injecting ads and/or content filtering. They are already improving the services their customers pay for. Offsetting that (relatively low cost) with some "bad form" advertising probably won't get a second thought.