I absolutely agree.
> And it doesn't require a smartcard either.
There are many good reasons why a counterparty does not trust you (fully) with a set of keys.
The biggest one is keys that allow financial transactions or billing events to happen: It makes the "I lost my password" defense for friendly fraud much less credible. Another can be to discourage sharing of a service (i.e. "account sharing").
Now there's two ways to keep "your" keys safe as a service provider: You build a fully locked down platform and only allow devices sold and made by you to attach to it (and play your content, use your phone network, transact on your payments network etc.), or you standardize the interface to the "key jail", keeping the rest of the device open and accessible to independent security research.
You can call such a tamper-proof device holding some issuer's private or symmetric key any way you want – functionally, it will be very similar to a smartcard.
The now reformed SBC/AT&T is doing something similar - only devices on this list[0] can connect to their VoLTE network. Without registering for VoLTE, the phones will not be able to connect to the network.
Even if a phone has full VoLTE compatiblity (the OnePlus 6 series, for example), if the manufacturer does not work with (read: pay) AT&T for certification, it will not be allowed on their network.
This is illegal under California SB822[1], which among other things prohibits the blocking of "nonharmful devices" on networks - but AT&T, along with the other major carriers, are currently acting like this doesn't exist until they're forced to by abide by it by a court of law.
[0] https://www.att.com/idpassets/images/support/wireless/Device...
[1] https://leginfo.legislature.ca.gov/faces/billTextClient.xhtm...
There was already a battle between AT&T and people who dared connect phones they actually owned to the phone network, and it ended well for the general public and badly for AT&T. The cell network should not get to determine what people attach to it; it should just pass data back and forth.
(In an ideal world, the cell network would have absolutely nothing to do with phone numbers, either; it would just pass data, and phonecalls would always happen over encrypted channels to your actual phone-number provider.)
> the concept of SIM cards is a net win for everyone, in my opinion
Public/private key crypto doesn't require a card that can also do other secret operations. And it doesn't require a smartcard either.