I have seen a few run on smart phones, it's being experimented with for sure.
I have read about them on fsxnet, I'm pretty sure someone ran Mystic on a smartphone off and on. I run it on several Raspberry Pis and have since 2014
or so. The Pi is ARM based, but Mystic is setup for x86, Mac, & ARM. It's still being developed and has servers like syncronet for most stuff. You'll find:
http://www.mysticbbs.com/ is the main source and the wiki is at:
http://wiki.mysticbbs.com/doku.php
I'm at bcw142.zapto.org (all standard ports) so 80 for http. That one is on
a raspberry Pi under Raspbian Linux.