I am using firmware to reference the entire mobile operating system, from the kernel and radio interface libraries all the way to the crapware applications installed by mobile carriers.
On Android devices, the best analog to the BIOS would be the bootloader. Since most Android bootloaders are locked to prevent unsigned kernels from running, they are updated during OS updates. See http://www.extremetech.com/computing/120771-what-is-a-bootlo... .
I was thinking that "subject to the approval of the carriers" was a legal requirement, along the lines of anything that could alter the operation of the radio would have to be approved. The hope being that a thin layer that deals directly with the hardware could be subject to approval, but the rest of the stack could be updated without approval.
On further reflection, I suspect it's more of a contractual obligation, and that neither party is all that interested in keeping 6 month old phones up to date. It's a shame, because Android developers can't reasonably expect ICS to be widespread for at least a year or longer.
On Android devices, the best analog to the BIOS would be the bootloader. Since most Android bootloaders are locked to prevent unsigned kernels from running, they are updated during OS updates. See http://www.extremetech.com/computing/120771-what-is-a-bootlo... .