>>> In fact, here's a patch with that very change.  Does
>>> it make current 2.6.0-test kernels work "out of the box"
>>> again with your USB modems?
>> 
>> Yes, it works with ELSA Microlink USB. Thanks.
> 
> Hmm. Too early. I get either a "acm: probe of 3-3:2.1 failed with error -5"
> but it works or a 
> Unable to handle kernel NULL pointer dereference at virtual address 00000008
>  ...
>  EIP:    0060:[usb_driver_claim_interface+67/112]    Tainted: P
>  ...

Well, the "it works at all (without the sysfs write)" is
what that patch was about -- so it's still a clear win!

But cdc-acm probe() is pretty broken, and I'm told it's
had strange behavior in various other cases for a while,
including some oopsing.  Like this; not a new bug.

Try this cdc-acm patch.  One user reported that it made
oopsing go away, the bogus probe() errors stopped, and
even the /proc/bus/usb/devices listings were finally
right (both interfaces now claimed by cdc_acm).  Plus
it should stop the pointless hotplugging of "cdc_acm"
for Ethernet devices (including MSFT's RNDIS).

- Dave