This is a user to user only forum, so you're not asking anyone at Apple your question. We have no idea what Apple may be working on. But your question also assumes everyone else is having the issues you are having and that is most definitely not the case. If it was, this forum, the most visited forum for all things iPhone would be littered with posts about this and yet it's not. I have no echos at all on iPhone 16 Pro or 16 Pro Max using AT&T on both phones on speakerphone.
There are lot of variables involved. It could certainly be an issue on the AT&T side, but usually carriers just want to get you off the phone and lay blame anywhere, but with them. You may need a carrier update too. You say you've tried ALL the fixes. We can't guess what fixes you've tried, so perhaps detail them.
A couple questions:
- Have you tried a forced restart on your iPhones --> Force restart iPhone - Apple Support
- By chance do you have any bluetooth speakers/headphones, powered on, which are connected to your phones at the same time you are trying use the speaker function during a phone call?