No, you will have to use the one from your current phone before you send it back.
Wooo! I just got my 7 Plus in the mail yesterday and I am in love! To answer your question though, iPhones purchased from us will have a new inactive SIM card already in the device. You can either use this SIM card or take the SIM out of your old iPhone and use it in the new phone. If you want to use the new SIM card, you can contact our customer care team to update the systems so that your number will be moved to the new SIM.