I don’t deal with the radio protocols that handle audio at all, but I’ve rarely experienced half-duplex audio on any of the phones I’ve used or made.
Sometimes, cell configuration can cause problems like that - you could try reporting it to your carrier.
-D/a
The only full-duplex cell phone speakerphone I’m aware of is the old Samsung BlackJack II. I’ve used it exclusively for years and it works great. Be sure you’re aware of what full-duplex really means…
I just had a lengthy call using bluetooth headphones. It sure seemed like incoming sound was suppressed while I was talking. Could be the result of “phone noise cancellation”, which is a setting buried under accessibility. I’ve turned it off, let’s see if that makes a difference.