Can you bookmark directly to the main screen on an iPhone?

Not as a standard iPhone function, but I have requested custom Home icons. And there may be modifications and hacks via the web for this purpose.

From what I've been reading online, there is a group of highly dedicated hackers working together to solve this problem.

Someone just recently created a pretty solid screenshot app for the phone (yes, in the phone, non-web app).

This is all the precursor to the near future. If Apple won't provide it, others will.

So to answer your question, not right now... But soon enough, soon enough.