Can anyone help me with this one:

If I take my unlocked AT&T curve which I use on Rogers (with a BIS setup through Rogers) to the states and put in my AT&T sim with pay-as-you-go with data option, will I be able to access my e-mail which is set up on the BIS from Rogers? (or do I need a BIS set up through AT&T).

I believe that you would need both an AT&T BB data plan and to set up the e-mail through the AT&T site.

You would need an ATT BB dataplan if you change SIMS. You will also need to set email up in ATT's BIS. There is no pay-as-you-go BB dataplan in the US AFAIK.