Comment # 9 on bug 914661 from Martin Pluskal

(In reply to a b from comment #8)
> systemctl status mgetty@ttyS6
> mgetty@ttyS6.service - mgetty on /dev/ttyS6
>    Loaded: loaded (/usr/lib/systemd/system/mgetty@.service; enabled)
>    Active: active (running) since Mo 2015-01-26 15:23:39 UTC; 54s ago
>      Docs: man:mgetty(8)
>  Main PID: 17622 (mgetty)
>    CGroup: /system.slice/system-mgetty.slice/mgetty@ttyS6.service
>            ������17622 /usr/sbin/mgetty /dev/ttyS6
> 
> ttyS6 works for me.
Thanks for confirmation, I will request maintenance update.
> 
> why is the symlink to /dev/modem a problem ?

There is BindsTo=dev-%i.device in unit file related to device, where /dev/modem
is afaik not considered to be device by udev/systemd (although symlink is
generated by udev).