According to research from Bain & Company, visits to a US bank branch are twice as likely to annoy customers as handling transactions on a mobile device. Gerard du Toit, a Bain partner who co-authored the report, estimated that each teller transaction also costs $2 to $3, compared with a dime for the same service at an ATM and just a few cents via a mobile device. Mobile devices are helping with customer retention as well: People who use their bank's smartphone app frequently are 40% less likely to switch banks than those who do so only rarely, according to the study.