I have PPC4100 but i live in HK. In my area have band 900MHZ but PPC4100 have 850Mhz. I want to update my radio stack or chance band to 900Mhz. Pls Help Me! Thanks

You can't.

The GSM bands are hardware specific and cannot be changed using software.

you will need a serious hardward mods to be able to achieve that.

u will proobably need to know someone that has an sp-230 the anixtek thinggy that has the 900 mhz gsm if u do know someone or if u have someone i will give u a proigram to dump the rom this will not caus any harm or risk to the pda jsut read.

basicly u will be using the anixtek rom on your audiovox.
thats it.