As far back as June 2010 there was chatter about Toshiba's new 128GB Nand flash memory modules. But currently the iPhone maxes out at 64GB and famously has no expandable memory option. Most people think 64GB is enough. Still, after the iPad went to 128GB, some folks were itching for a 128GB iPhone, even if it would carry a price tag of over $500 (and maybe $600) with a contract.
We didn't get a 128GB 5S (and the 5C only goes up to 32GB), but maybe we'll get a 128GB iPhone 6.