Question [Q] Is HSPA band controlled by kernel/firmware?

Hi, I have Sony Ericsson wt19i bought in europe. It supports HSDPA 900 / 2100 band. Sony Ericsson has a satelite model wt19a, which supports american HSDPA 850 / 1900 / 2100 - WT19a.

Is this HDSPA band controlled by Kernel/firmware or it is determined purely by hardware. Is it possible to enable HSPA 850/1900 on my wt19i by chaning the kernel or firmware.

I did try flashing a stock firmware for wt19a, but it did not help...