You can process credit card transactions anywhere you can get a mobile phone signal. This service offered by MobileCharge. This system combine a mobile printer, an online payment processing service (Authorize.net) and a smartphone to do this. There are 3 different versions - Palm OS (Treo 600), Windows Mobile (Samsung i700) and Blackberry.
This looks like a very convenient solution for trade shows, fairs and other events when you can’t get a traditional credit card system in place. The MobileCharge website hasn’t been updated for a while, though, so buyer beware.
