IIRC that
64k was in fact 56k with 8k for overhead.
I had one,
and it would kick in a second channel if you pushed it, for
a whopping 112k. Metered, came out to about $500/mo.
My first ISDN experience was in Swaziland, 2003. There weren't many
countries in Africa that offered it, actually. As tiny as Swaziland
was, I was surprised they did.
I just liked it because the dial-up was instant and it didn't "sing
the modem song" :-).