Skype ; Because my R.I.P. grandma was using it to talk to her relatives overseas just like she would use a phone, but it didn't cost an arm and a leg (unlike phone calls).
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A genius product ripped my Microsoft. Have you used Microsoft Teams recently? Bad UI, hard to configure external hardware and good level of incompatibility, missing the good old "Echo / Sound Test Service". At a point I even installed Skype of my old Android but was sucking up too much battery.