We recommend you always print your boarding passes.
While many carriers do support paperless boarding passes, there are airports that still lack the infrastructure required to process them. So, play it safe: print your boarding passes before you arrive at the airport. (If printing at home is not an option, then consider going to a local internet café or library; hotels will also often offer this service to its guests. Worst case scenario, you can always look for places on the way to the airport or at the airport itself.)