If you are returning 1 of 2 regular STB's, customer service will need to know the GUID (its a letter/number string printed on the bottom of the STB) of the box you will be returning, so they can remove the right one from your account. Customer service will provide you instructions on how to return it.

ginpr - You will receive no channels without an STB, but you can do what VinnyM69 is doing and connect two tv's to one STB. Both of them will get a picture, but they will always be on the same channel, and you will only be able to change the channel from the room that has the STB in it.