The last iPhone 3.0.1 update that fixes that (over-hyped) SMS bug is again 297MB large. So it is a full OS image for something that is probably just a small fix in the SMS subsystem of the iPhone.
This is just so silly. With 40 million (or so) iPhones sold this adds up to an insane amount of wasted bandwidth.
If Apple and Google were still friends then maybe they could have used http://dev.chromium.org/developers/design-documents/software-updates-courgette instead.
I'm sure that would have turned that 297MB into something of at most a couple hundred KB instead.