Comment 7 for bug 129433

Two more notes:

Note 1:
Problem #1 might be just a duplicate of https://bugs.launchpad.net/ubuntu/+source/linux-source-2.6.20/+bug/88746.
Apparently just too many people are lamenting the need to disable ehci_hcd to get things working (and obviously these are just a minority: the most will not even know about ehci and will just think that USB is still not well supported in linux and that they'll need to just avoid it given that their USB gadgets cannot be used).

Note 2:
If linux does maybe not yet shine on ehci, sure it shines in the ability to control what is going on.
So there is a very good news. As a workaround, rather than blacklisting ehci_hcd alltogether (that results in the loss of support for USB 2 peripherals), one can just selectively disable it on some hubs.

For instance, in my case, I can

sudo sh -c "echo -n 0000:04:00.2 > /sys/bus/pci/drivers/ehci_hcd/unbind"

and get my umts thing working. In principle it should not be too difficult to do it automatically when the device is detected.