HTC Touch Pro Sprint?

[xelasha]

Hello everyone. I'm interested in buying a HTC Touch Pro from the US.
It's for a really good price but I wish to know why are the Sprint branded phones a lot cheaper than other branded phones? Is there a missing feature?, can you flash them? And is Sprint some sort of US phone company provider or is it a different kind of distribution of the HTC Touch Pro?

Also I have never flashed a smart phone (only SE phones) before so if somebody could give me an up to date guide (Or a guide that is old yet is still the same guide everybody uses) that would be helpful.

And also after flashing will my Australian sim card work? Will I still be able to get the full features as if I bought it here?

Sorry for the noob questions, I just want to be sure of all this before buying.
-xel