The man pages mention that:
"oFono is controlled through D-Bus;
for example, one can tell ofonod to send
AT commands over /dev/rfcomm0 by calling
the D-Bus method org.ofono.at.Manager.Create"
Well this is embarrassing. That manpage is completely out of date.
Please forget whatever you read in it.
USB Modem detection in oFono is handled by plugins/udevng.c. Generally,
things just work. However, you might have a device that isn't
supported. At least the vendor id / product id you mention are missing