++ Phone Plan help! NOKIA ++ Best answer 10 pts!?

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I have just purchased the NOKIA 6500 Classic at an optus phone store, then realised I want to go on a Virgin Free to V CAP.
Does anyone know if I can return the phone to the optus shop?
It is brand new, still in the box, I have the receipt and bag and only bought it yesterday.
What should I say when I take it back??

THANK YOU!