Hi. I have decided to return the retina mini...I am going to go for the Air. The screen is more vibrant and the larger screen is better especially since weight is down. Anyways, the mini retina I bought was Verizon. When I return the mini, can I keep the verizon sim card? The Air I bought was a Sprint one since it was the only one in stock, but I had to lock in sales price. Thanks!