Looking at the tech specs on Apple's website, both the iPhone 6s and the 7 use a nano-SIM. I'm on AT&T with a 6s. If I order a new 7 from Apple, will I need a new SIM or can I just swap from my 6s? The reason I'm asking is that even though they are both nano-SIM, I have heard that sometimes a new SIM is needed to take advantage of new network features (such as advanced LTE). Thoughts?