yes buy the device once at $30 and keep it for ever.
use it when you are in aruba and buy a plan that suits you best.
from what i have heard and read 4gb is the popular plan and as liz says that is about $40
it uses a cell signal, that is how it picks up the wifi.
so even if your resort is loaded with wifi modems/routers (i do not know the difference) from setar, the mio device will pick up the internet using a cell phone signal
i start my converstions with brighthouse (our wifi and cable co) the same way that you do!!