Economists have long known thatfinancial services have benefits for users by allowing themto smooth consumption, save for bulky purchases, etc. Butthe recognition of their importance even for people withrelatively low incomes those earning one to two dollars aday, for instance is relatively recent. This recognition hasbeen spurred by a better understanding of the financiallives of the poor, and of the critical role played byuncertainty and volatility. The objective of this case studyis to describe the design and implementation of WING, aCambodian mobile-phone-based payment system. The product hasbeen successful in providing access to formal banking to thepreviously unbanked in Cambodia. The following sectionspresent the problem of financial exclusion, how WING meetsthis problem by providing a mobile banking network, theunique aspects of WING s design compared to other products,challenges in achieving technology adoption and otherconstraints faced by the product, and how WING has respondedto these challenges throughout implementation. Finally, thecase study presents lessons learned and behavioralapplications for future products.