When you can download books to your phone.
I am totally in love with this. I’ve got 6 novels on my phone now and when the Kid needed to read War of the Worlds for school we put it on his phone too.
Mostly it is books that are past the copyright date, but there are a few contemporary writers who put things up too. I’m fine with the classics though, being that I am a serious anglophile when it comes to reading. I just finished Wilkie Collins No Name