Just exchanged my T-Mobile iPhone X for Verizon one. Inserted my T-Mobile card and not only does it sound better on phone calls, it is also useable on any carrier due to better modem.
While I'm a culprit in the huge vocal minority complaining about Intel modem inferiority, I do think making a new thread for this over and over isn't helping.
Apple will not care unless people speak with their money.
I have not, and will not, get a newer iPhone than the 7 Plus until they give me a modem that can function as well as my V30+.