They use mobile phones in areas without electricity in some African nations I think, its possible to exchange but the confirmation of the transaction is probably not the best in these remote situations.  I hear of women in Afghanistan using Bitcoin and gaining new found freedom from the ability to retain wealth and value to their livelihood that was never possible before with physical currency only and the constant violent threat they live under.   Whenever there is a utility and gain, commerce enabled by the operation of a blockchain or any exchange of value then it becomes justified and more likely to continue in its value long term.   
  Ultimately FIAT betrays all who have trusted in it as its raw background of being bound to politics and all that weakness rather then trade and security of value wil become apparent, by the time its obvious it will be over at that point so its a good thing BTC is already here as a possibility to anyone who wants it.