An unexpected obstacle about the privacy-protective MVNO that I heard about from someone who was investigating this is taxes on "telephone lines" that the MVNO is supposed to pay whenever it "activates" a "line". It may be difficult to reconcile this with changing subscriber identities every day (assuming you can get ahold of devices that change device identity every day).

Whenever I talk about this I say: it's too late to change the cell phone network cheaply now (though we should still be vocal about the problem and not give up: we shouldn't accept that there is someone who knows where almost everyone is almost all of the time, which is the case today). If you're designing a new communications system, make sure that it starts with privacy protection and user and device anonymity, and layers optional identity on top where needed, rather than the reverse! Let's not be saying in 2030 "oh, if only people in 2015 had thought about the privacy issues with this technology...".