First of all, SMS is based on a common protocol used across carriers. Each carrier does not need to individually support each model of device, and vice versa--

First of all, SMS is based on a common protocol used across carriers. Each carrier does not need to individually support each model of device, and vice versa-- as long as both the phone and the carrier support the decades-old standard, your messages will get routed to a SMSC and from there to the recipient. The carriers are not involved in this process at all aside from setting up the industry standard protocols involved. It's also all or nothing, there's no identifying characteristic on a message saying "this was sent by that iPhone we don't want to support anymore". Additionally, 5G SMS does generally go over IP as SMSoIP: https://www.iplook.com/info/what-are-the-changes-of-sms-in-5g-era-i00037i1.html https://www.iplook.com/info/what-are-the-changes-of-sms-in-5...