Affirmative on both counts. We have used ours in Alaska and Hawaii from the ship (Princess and NCL). No problems. Your calling plan determines the charges which may apply and location determines if you can get through of course.
And one has to be within reach of an antenna. (G) For example, it won't work out in Glacier Bay. But it should work in most ports. And depending on your plan, could be included in your coverage. We found them useful when in port to find each other. Or even on ship in port - as long as one is in range.