Since you have the treo you will want the vision, that’s a given. As far as what kind of plan you need, that all up to you. How many min do you see your self using? Looking at past bills is the best way to see your calling habits. Start with a plan and then add options like vision, PCS to PCS, ERP (equipment replacement Program, Get this option. If you loose your phone or break it we will send you another one. It's only 4.00 a month and it's a whole lot better than buying a new treo for full price), 7pm night and weekend min, exc. You also mentioned roaming... it think. You said something about Verizon... If you need off network roaming (real roaming) you may buy bundles of them for 10.00 and they include 100 min you can use on someone else’s network. These are stackable if you need more.
Now as for your phone number, you can have a phone number from a different area but you will need an address to point that number to. This is called a coverage address it can be different than your billing address.