Opening a new account and cancelling within 30 days

[Hoof]

It might not be the most legit way to get the phone but I was planning on opening a new line and then canceling within the first 30 days and then just activating the phone thought my current line.

I went to bestbuy and the girl told me I would have to return the phone first before they canceled the line. Can anyone confirm this? I ended up having to leave but plan to return later today.