>>erohea+(OP)
What I really want is both, a larger phone (for me happens to be iPhone) for "most of the time" and a smaller phone for occasional use. I want them to have the same phone number and keep data in sync, basically like two extensions of the same line. However, I'm not willing to pay my carrier a premium/additional monthly cost just to have two phones that cannot be used simultaneously.
Much of this is able to be done with wifi, but not via the cellular networks (without additional costs).
In other words, there is no ideal one-size-fits-all option, and I'd be willing to pay for additional hardware to give me choice of what to carry at any given time, but I do not want to pay Verizon just for the privilege of having a 2nd SIM provisioned (and I do not want to swap SIMs).