I am using an USB phone that is in fact a so-called "sound card" based on the 04b4:0307 chip.
In fact, I have two different phones using 04b4:0307 and in fact I have a sound USB key too.
This, I believe, is the start of why they call 04b4:0307 "ubiquitous" (instead of oh four bee...).
But not "eternal". The mike worked in Ubuntu 9.10 and 10.04 but not later ([email protected]).
"not working" means that 04b4:0307 shows in Sound Preference but that its vu-meter is mute.
I have posted the full lsusb and the result of tests in various systems here:
http://www.papou.byethost9.com/tmp/1043601.html
Note: Tests done on VirtualBox (thankfully). But UbuntUnity no longer works on VB, so I used the LinuxMint equivalent. ?hat's fate.

I could not find any problem report close enough. What should be my next step?

I believe the problem occurs in module snd-usb-audio. One thing I might try if I knew how is hacking a DEB with its 10.04's source. I can hack DEBs. Any hint welcome on how to make a DEB overriding a kernel packed module.
I mean that the newly installed module should have precedence, be loaded instead, the module installed with the kernel.

TIA !