I suppose it depends highly on hardware. Many areas in the world don't have stable mobile networks, so there are not much possibilities for internet infrastructure, though fiat money is being used everywhere, and fiat money is actually produced using technologically advanced equipment (paper and paint should be of high quality, many picture details and watersigns need to be performed with high accuracy etc). The same is true for bank cards. So there is a way for bitcoin and other cryptocurrencies to become usable in areas with low network coverage: it may be something like mass produced e-wallets with displays (nowadays there are enough technogy resources to start mass production of these things yust in the way fiat mo ey is produced). And, transactions go offline until there is a way to join global network for any of the devices in the area, then data is uploaded and added to blockchain.