I can't speak for all of us uncouth Americans, but I generally end phone conversations with well wishes and a goodbye.
If you think Americans are bad, try doing some phone conversations with Japanese people and see how they end...<abrupt end of conversation...delay...dial tone>.
It took me a long time to get used to that...
Even in my Japanese phone conversations I try to end with an obligatory "Bye-Bye" or "Ja, Ne?".
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