I do not know how native English speakers colloquially pronounce the question "Whose is it?". What would the IPA of the sentence be like? An IPA keyboard is here
Update: you could record the sentence in Forvo if you want to provide a great service to the world! You'll need to open up a free account; it takes just seconds if my memory services me right.
By the way, are American and UK pronunciation the same in this case? I know that in the case of "is n't it?" are different.