Only time I ever used one was when I was chaperoning a family friend's two kids across the country (I was in college, kids were 11 and 13) back in the mid-90s. They asked about the phone, told them it actually worked, they really really really wanted to call their mom, so I told them we could call them around the halfway mark (ATL-LAX is a pretty long flight, to be fair). Let them talk for about 3 minutes which I recall was somewhere north of $10. I thought it was pretty crazy, but ngl it was kinda neat being able to call people from the air.