As one point of anecdata, the IRS refused to honor my Fi phone plan because it didn't have my name and mailing address registered on it (or at least to their satisfaction). I don't know if they still require a post-paid cell phone plan for their auth scheme or not, because I gave up trying to make it through after about 6 months of requesting magic codes through the USPS
Anyway, that's a lot of words to say "MVNO" is for sure not identical to "any other cellular network" for a certain class of interested parties, in the same way that pre-paid credit cards are not the same as other credit cards
