The commercial use of the Internet for service provision has deeply changed the environment where human-computer interaction takes place, as Web interfaces are now integrated in multi-platform service provision. This paper presents the results of a study of a multi-channel Portuguese bank, making use of both Marketing and HCI methods and concepts, to understand customer usage of the different service platforms. The study involved in-depth interviews, focus groups, a web survey and a telephone survey with bank customers.The study allowed the identification of the most important interaction experience requirements for this multi-platform service, and how they are influenced by user profiles and service characteristics. The results also show that Customer Experience Requirements (CERs) have a strong impact on customer choice and usage of the different service platforms and can be better captured with Essential Use Cases (EUCs), as they are technology independent. Designing a multi-platform service interaction should therefore start with a higher level of abstraction that allows a multi-platform, customer experience and essential use case perspectives. With this integrated approach, the Internet service can therefore be designed in order to best leverage its capabilities and its complementarity with the other service platforms.