there is no "guessing", the person giving you their number can also tell you which platform they are on (in my country 99,9% of the time it will be Whatsapp).
making an antitrust case on the basis of "I don't want to guess" seems weak, but law can always turn out counterintuitive
> the person giving you their number can also tell you which platform they are on
That... doesn't solve the problem. We don't need fragmented messaging systems, we need the world's largest company to lay down some rules and abide by them. Right now, the existence of iMessage is predicated on the poor performance of traditional SMS messaging. It wouldn't surprise me if the United States (much like Europe's antitrust council) forced Apple to standardize their proprietary alternatives. There's nothing counterintuitive about that to me.
This is pretty different to the international dynamic, as MMS often comes at a surcharge in many non-US markets, but here unlimited MMS has been included in most plans for a very long time, so there's not even a "hey, you are costing me money" stigma involved like there was in the bad old days decades ago.