Well, it's not just selling phones that is the issue but selling SIM cards. That's closer to the "Comcast only supports cable modems with Mac addresses they've

Well, it's not just selling phones that is the issue but selling SIM cards. That's closer to the "Comcast only supports cable modems with Mac addresses they've identified and Command & Control functionality they need" analogy. (Which are things that cable modems support. Cable company operators can force certain cable modem operations similar to the way SIM cards support such things.) But also, it really isn't all that bizarre, it's got long precedent: For most of a century all phones were leased and the phone company controlled every bit of hardware on the network. That's not even the distant past, that's still in living memory, my parents grew up in households with leased phones. It took major anti-trust/monopoly breakup work to change that. So far the "use whatever phone you want" is the anomaly in the history of phone networks. (Cable companies too; most of their history all of their equipment was only leased and the era of being able to buy your own set top boxes and/or cable modems is a relatively brief anomaly versus the longer history of those networks.) The US is back down to only two/three major cell carriers (no matter how many "brands" you see; so many of them are just resellers), depending on how you want to count them (by network compatibility: two; by parent company: three). It may be time to trust-bust again.