I have problems also pretty much exactly as you describe them. I am on the T Mobile network also and live pretty close to the Canadian boarder, but don't cross over.
As I'm talking to people sometimes one of us or the other will cut out... sometimes both of us at the same time. The duration varies, but can last multiple seconds... long enough the other party gets frustrated and hang up. Sometimes switching to speaker helps, but not always. I've tried changing some preferences on my phone (Wifi enhanced calling, Network preferences (NR/LTE, etc) but nothing seems to really help.
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