You're right "soda" and "pop" are interchangeable words for the same thing. Some parts of the country use "pop" and some use "soda" when refering to soft drinks. Here in Michigan we use
"pop" when asking for a soft drink, if you hear someone ask for a "soda" it's a dead giveaway they are from out of town.
Since we seem to have shifted the discussion to cultural differences, maybe you could answer a question for me.
Just what the heck is a "vegimite" sandwich?