[dmm]

I'm from Philly. (That's Philadelphia, Pennsylvania for you non-USAers.) We say "soda" definitely. Also most Washington, D.C. area natives say "soda." I'm fairly sure that it is "soda" throughout the entire Philly to DC megalopolis. I think "soda" extends north to NYC, but changes to "pop" by the time one reaches Boston. And I'm fairly sure that it changes to "pop" pretty suddenly south of DC.