Yes, but US Mobile is an MVNO, so your coverage is the same coverage as the underlying network. In Mazama, you can choose between AT&T (Dark Star) and Verizon (Warp). The very nice feature with USM, is that you can teleport between carriers - keeping your same plan and account. So you can just switc...

Not that I'm aware of. Try OXARC in Okanogan.
They might only do tank exchange.