Hi, I am planning on switching from AT&T to Verizon but I am on someone else's plan . I want to be able to keep my number . Can I do that when I buy the phone now online or do I have to do it in store ? Also if I pre order the iPhone 6s Plus will I have to wait for my service to start or can I switch over my current phone and use it with Verizon until my new device comes in ?