I bought a new iphone7 jet black from Best Buy 256 gig for 150.00 dollars off. On sale great price. On phone its listed as model MN8W2LL/A . Can some one tell me if this is a1660 or a1661 or a1778 or a1784? The reason I ask is from what I read on apples web site is a1660 an 61 when unlocked can be used on all carriers but 78and 84 can't. Thanks