We consider 311 non-emergency contact centers as city-level service integration initiatives. By using a cross-case study of 311 centers at New York and Philadelphia, we found critical success factors and challenges of service integration. This paper suggests multidimensional (technological, organizational, and cross-organizational) implications. Stable operation of 311 centers requires timely investment in having a technological system best fitting for service integration, but city governments with limited resources should instead consider adaptive strategies for overcoming under-equipped situations. While the lack of interoperability remains as a critical barrier to system-level integration, customer service agents play a pivotal role in connecting non-interoperable systems to front office systems and back office systems. Thus training for qualified customer service professionals is key to the seamless operation of 311 contact centers. Turf guarding often raises cross-organizational concerns, but the top management's administrative and political support helps resolve inter-organizational conflicts. Based on these findings from the exploratory study, this article proposes significant ideas for further research on municipal service integration through 311 contact centers.