Sam can't provide App in their own 3G HSDPA and iPhone with both are launched in the same month competing against each other. It's called conflict of interest. Something has to give.
All smartphone competitors, NOK, Sam, Palm, MOT, LG scrambled to announce new products before iPhone launch to counter it.
BTW, AT&T delayed the HSDPA network build-out to work on 2.5G EDGE upgrade, aka Operation "Fine Edge".