I just think of the infrastructure changes for supporting USB 3G
modem.  Jesper Nordenberg mentioned in previous mail post:

<%
(Oct 6)
The modem seems to be detected as "usb-storage", but when initialized
it generates some error code -5. No /dev/tty* devices are created for
the modem. Apparently this has been a problem before with the Option
modems (see , but should have been resolved in recent kernel versions
(the HSO driver should be included in 2.6.27 and later). See
http://www.pharscape.org/hso.html for more info. The modem is detected
correctly in Ubuntu 9.04.
 %>

<%
(Oct 12)
We've obtained a Novatel Ovation MC950D modem. It's mounted as a
storage device in Linux and to get it to work as a modem it has to be
ejected and then "sudo modprobe usbserial vendor=0x1410
product=0x4400" has to be run. How do you do this in Android as
neither eject or modprobe are available commands?
 %>

The reason is that USB modem usually comes with extra storage where
the corresponding MS-Windows Driver & Utilities locate.  Thus, we
shall make changes as least for the following items:
- Introduce a customized /sbin/hotplug to monitor USB add/remove event
and send message to vold and helper applications.
- exclusive list for vold NOT to mount.  We shall not touch that
storage since it could be easily manipulated via usb-serial.
- usb-serial setup (modprobe with specific parameter), establish
connection, and let ppp connection managed by Android.

Further evaluation needed.

Sincerely,
Jim Huang (jserv)
http://0xlab.org/