Hi. i have only 2G old iphone, in fact jailbreaked.
i am with 2.1 firmware
my question is :

do i have to change firmware 2.1 to 2.2 and use the last Iphone_SDK too?

i know if i jailbreake with 2.2 will work, and develop. but
my question is, what happen if some body wants to install an aplicacion
with 2.2 if only have firmware 2.1 ?

thanks a lot !

If an app is built on the 2.2 SDK (which Apple recommends) it needs the 2.2 firmware.