I preordered an iPhone 6 Plus, and I currently own an iPhone 5. My carrier is AT&T in the US. When my new phone arrives, I may want to use it as a wifi-only device for several days before committing fully and transferring my AT&T voice and cellular data from the old phone to the new phone. Can I do that? Can I use the new phone like an iPod Touch, basically? Or is the phone unusable unless I activate the cellular plan? Thanks.