I'm moving to San Francisco next month and so I've gotta setup a new
cell # locally.

I own a Sony Ericsson W800i, it has sim card capacity so I should
technically be able to use it anywhere in the world so long as I can
get a sim card from the provider.  However, my boyfriend insists that
I'll encounter problems since all the providers in the states dun
support other phones/won't let you use phones not sold by them.

So my question is, if I'm to set up a new account in San Francisco,
with needs to call both locally and internationally, and I want to be
able to use my lovely W800i, which cell phone company could accomodate
that and still offer the best deal in town?

Any of them, theoretically, depending on where you go. I got an import
phone from t-mobile and have no probs at all. What you could do is get
a friend to unlock their phone and use their sim card, while they get
a new number + phone.

Thanks me2me2.
I'm already here now and I visited a Cingular store where I was able
to pick up a sim card and just popped it in.  Guess my bf was being
silly. :P