Public Mobile works a little different from the other carriers in that they will not let you use stuff that isn't in your plan. If you do not have international minutes, you cannot call international numbers. In my opinion this is better than calling...
Yeah, I think it would be very nice to have something along the lines of a 250 US text add-on, 5$-10$ whatever makes sense on Public's end. ( hopefully 5$ ). As far as roaming goes, that's a huge task that I doubt is on Public Mobile's todo list for...