T&T: Aircards-More Info please

[Bob/Myrna Siegel]

Our internet service at home  is via dial-up and we are satisfied.  Our
laptops can access the internet when we are in hot-spots, e.g. libraries, some
marinas, etc.  We can also dial our ISP via phone when away from home if the
ISP has a local or toll free phone number from that area. Exactly what are
aircards? How does one pay for their service, i.e. are charges per minute or a
single up-front charge when purchased ?
Bob Siegel Annapolis