Depending on your carrier, you could do this without swapping SIMs -- as far as I know, all of the Big Three in the US (Verizon, T-Mobile, AT&T) all have "number-sharing" programs normally reserved for things like smartwatches. In fact, Palm specifically advertises that they work with Verizon and T-Mobile, and proposes alternatives for other networks (https://palm.com/pages/companion). If you're serious about this, it sounds worth looking into!