Sebastian Siemiatkowski, CEO of Klarna, speaking at a fintech event in London on Monday, April 4, 2022.Chris Ratcliffe | Bloomberg via Getty ImagesKlarna's CEO is so bullish about artificial intelligence that he sees it changing the way the fintech's 100 million users bank every day.On Wednesday, Klarna — a pioneer of the popular "buy now, pay later" (BNPL) payment method — is announcing the launch of mobile phone plans in the U.S. via a partnership with telecom services startup Gigs. The move f...