I use an iPhone thats i got in 2022, on carrier signal, over regular voice calls, not wifi call or anything like that.
I’ll use a pair of true wireless jbl earbuds. I admit, I never really stopped to test if it only happens when connect to the earbuds or not.
Both houses do have landlines, but I haven’t used the landline for any of these conversations. It’s pretty much only used to field telemarketers or for things like the ac repair guy and the church people.