It's always been soda. Although if you didn't want someone to come back with a nasty-ass Pepsi or Coke Zero or something, you'd have to be more specific. At least, that's how it works in Texas.
I don't know if this is specifically regional to a particular part of the coast, but, folks in california call it "pop". Same with northerners (PA, NY)
im from ny and ive never referred to soda as "pop"
In my country we call carbonated beverage sold from vending machines a Zionist Jewish conspiracy to sap and pollute the purity of our natural bodily essenses... That and Pop.
I never heard called soda before until my friend from California called it soda and got all butthurt over it when she heard me say pop. Needless to say massive trolling ensured.