Like the other residents of the British Isles have pointed out, we tend to say 'fizzy drink' or the brand name.
But some people, I want to say of an older generation, but it could easily also be geographic, might use 'pop' or 'fizzy pop', but only really with reference to children drinking it. You wouldn't, for instance, order a vodka and pop. (well, I personally might, once lemonade becomes two syllables too many...
)
On a side note, in my family at least, we tend to use juice as a generic name for any cold, unfizzy drink that's vaguely fruit-based. Which can get confusing when you have orange squash and orange juice in the house.
Helga
